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ENGINEERING 
ECONOMICS 


By 

J.  A.  L.  WADDELL.  D.Sc..D.E.,LL.D. 
Consulting  Engineer 


ENGINEERING  ALUMNI  ASSOCIATION 

SCHOOL  OP  ENGINEERING 

UNIVERSITY  OF  KANSAS 

LAWRENCE 

1917 

(DISTRIBUTED  FROM  THE  DEAN'S  OFFICE) 


ENGINEERING 
ECONOMICS 

A  Series  of  Lectures  Delivered  Before  the 

Students  of  the  University  of  Kansas, 

School  of  Engineering 

FEBRUARY  9,  1917 


In  Three  Parts: 

I.    THE  GENERAL  PROBLEM 
II.    ECONOMICS  OF  BRIDGES 

III.    ECONOMICS  OF  OTHER  ENGINEERING 
SPECIALTIES 


TA  153 


ENGINEERING  ECONOMICS 
LECTURE  I 

The  subject^of  these  lectures  was  not  chosen  by  the  speaker,  but  was 
allotted  to  him  by  your  worthy  dean  of  engineering,  Prof.  P.  F.  Walker. 
It  is  a  topic  that  very  few  engineers  would  care  to  undertake  to  cover  in 
three  short  lectures,  not  only  because  of  its  complication  but  also  on 
account  of  its  vast  extent,  permeating,  as  it  does,  every  branch  and 
division  of  engineering,  great  and  small,  and  all  work  that  is  either  directly 
or  indirectly  connected  with  the  profession.  On  that  account  the  speaker 
debated  for  some  time  before  accepting  the  invitation  to  address  you  on 
the  specified  theme;  for  he  would  greatly  have  preferred  to  take  some 
subject  in  which  he  has  really  specialized,  primarily  because  he  could  do 
himself  more  credit  thereby,  but,  it  must  be  confessed,  also  because  he 
rather  dreaded  the  immense  amount  of  preliminary  study  and  research 
requisite  to  a  proper  presentation  of  the  matter.  As  far  as  his  specialty 
of  bridges  is  concerned,  he  is  able  to  treat  the  question  of  economics  quite 
readily,  because  he  has  been  dealing  with  it  and  writing  about  it  for  more 
than  three  decades;  but  when  it  comes  to  discussing  economics  in  other 
lines  of  engineering,  he  feels  very  much  at  sea — so  much  so  that  he  im- 
mediately decided  that  he  would  have  to  divide  his  discourse  under  two 
main  headings, — viz.,  general  features  which  pertain  to  engineering  of  all 
kinds,  and  detailed  features  relating  to  the  numerous  specialties  into 
which  during  the  last  half  century  the  profession  has  been  segregated, 
and  also  that  he  would  have  to  seek  assistance  on  the  latter.  Any  engineer 
of  years  and  wide  experience  in  one  or  more  lines  of  activity  should  be 
capable  of  handling  the  first  division,  but  no  man,  unaided,  could  ade- 
quately treat  the  second  division  in  more  than  two  or  three  specialties. 

Recognizing  this  to  be  the  case,  the  speaker  took  the  liberty  of  calling 
to  his  aid  some  of  the  leading  specialists  and  authorities  of  America  so  as 
to  supply  him  with  the  salient  features  of  economics  in  design  and  con- 
struction in  the  numerous  divisions  and  subdivisions  of  engineering  prac- 
tice. Acknowledgment  of  such  aid  received  is  made  throughout  the  text 
of  these  addresses,  usually  by  means  of  foot-notes;  but  the  speaker  deems 
it  advisable  to  state  collectively  at  the  outset  the  names  of  the  gentlemen 
who  have  so  favored  him  and  their  special  lines  of  work.  They  are  as 
follows,  the  arrangement  of  the  list  being  alphabetical  in  relation  to  the 
specialties: 

SPECIALTY  AUTHORITY 

City  Planning  CHAS.  MULFORD  ROBINSON 

Dams  ALFRED  D.  FLINN 

Electric  Railways  E.  P.  ROBERTS 

3 


371590 


SPECIALTY  AUTHORITY 

Engineering  Teaching  GEO.  F.  SWAIN 

Harbors  WM.  P.  ANDERSON 

Highways  W.  G.  HARGER 

Inspection  P.  S.  HILDRETH 

Mining  JAS.  W.  MALCOLMSON 

RaHroadin* 


Water  Supply  ALFRED  D.  FLINN 

To  all  these  gentlemen,  individually  and  collectively,  the  speaker 
desires  herewith  to  tender  his  hearty  thanks  and  deep  appreciation. 
Without  their  valuable  aid  these  lectures  on  the  lines  adopted  would  have 
been  impossible. 

It  should  be  noted  that  the  preceding  list  of  subjects  is  by  no  means 
complete.  It  is  limited  by  the  responses  from  the  "authorities"  to  the 
speaker's  appeal  for  aid.  On  the  whole,  the  profession  has  been  very 
generous;  and  while  there  is  evidently  a  lack  of  correlation  and  uniformity 
in  the  various  treatments,  this  is  unavoidable.  Moreover,  it  should  not 
be  objectionable,  indicating,  as  it  does  very  clearly,  the  personal  equations 
of  the  donors  of  the  information,  notwithstanding  the  fact  that  occasion- 
ally the  speaker  has  taken  the  liberty  of  materially  modifying  the  diction. 

Again,  the  incompleteness  of  the  list  of  subjects  is  not  a  blemish; 
because,  if  it  had  been  made  even  approximately  complete,  there  would 
not  have  been  sufficient  time  in  the  set  limit  to  discuss  all  the  topics  with 
adequate  fullness. 

In  one  sense  the  subject  of  economics  in  engineering  is  a  new  one, 
because  it  is  only  of  late  years  that  it  has  been  given  much  attention  by 
designers,  builders,  and  technical  writers;  but  as  far  as  the  speaker's  task 
is  concerned  it  may  be  said  to  be  an  old  one,  for  the  reason  that  the  said 
subject  has  been  systematically  and  elegantly  treated  by  Prof.  J.  C.  L. 
Fish,  of  Leland  Stanford  University,  in  his  excellent  little  work,  which 
bears  the  same  title  as  that  of  these  lectures,  —  viz.,  "Engineering  Eco- 
nomics". Although  that  work  covers  the  ground  in  a  satisfactory  manner, 
it  will  not  be  necessary  for  the  speaker  to  crib  from  it;  because  the  subject 
is  such  a  broad  one  that  it  will  bear  treatment  from  more  than  one  point 
of  view. 

As  far  as  relates  to  engineering,  the  term  "Economics"  has  been  defined 
thus  in  the  "Glossary  of  Terms"  of  the  speaker's  new  book  on  "Bridge 
Engineering"*,  —  "The  science  of  obtaining  a  desired  result  with  the 
ultimate  minimum  expenditure  of  effort,  money,  or  material".  It  is  upon 
the  basis  of  this  definition  that  these  lectures  are  predicated. 

GENERAL  FEATURES  OP  ECONOMICS 
When  determining,  from  the  standpoint  of  economy,  which  is  the  best 


*J.  A.  L.  Waddell,  1916,  "Bridge  Engineering",  Wiley  &  Sons. 

4 


of  a  number  of  proposed  constructions  or  machines,  one  should  compute 
for  each  case  the  four  following  quantities,  and  their  sums: 

A.  The  annual  expense  for  operation. 

B.  The  average  annual  cost  of  repairs. 

C.  The  average  annual  cost  of  renewals. 

D.  The  annual  interest  on  the  money  invested. 

That  one  for  which  this  sum  is  least  is  the  most  economic  of  all  the 
proposed  constructions  or  machines;  but  this  statement  is  truly  correct 
only  when  the  costs  of  operation,  repairs,  and  renewals  are  averaged  over 
a  long  term  of  years;  or  else,  for  a  comparatively  short  period  of  time, 
when  the  conditions  in  respect  to  wear  and  deterioration  at  the  end  of 
that  period  are  practically  the  same  for  all  cases. 

The  principal  economic  investigation  that  occurs  in  engineering  practice 
is  that  of  determining  the  financial  excellence  of  a  proposed  enterprise. 
It  consists  in  showing  by  proper  calculations  its  first  cost,  the  probable 
total  annual  expense  of  maintenance,  repairs,  operation,  and  interest,  the 
advisable  allowance  for  deterioration  or  ultimate  replacement,  the  prob- 
able gross  income,  and  the  resulting  net  income  that  can  be  used  in  paying 
dividends  on  the  stock  or  other  profits  to  the  promoters.  Whether  any 
proposed  enterprise,  after  being  thus  figured,  will  prove  profitable  will 
depend  greatly  on  the  state  of  the  money  market,  the  size  of  the  project, 
the  probabilities  of  future  changes  in  governing  conditions,  and  the  per- 
sonal equation  of  the  investor.  Generally  speaking,  if  the  computed  net 
annual  profits  on  the  total  cost  of  the  investment  (over  and  above  all 
expenses  of  every  kind,  including  maintenance,  repairs,  operation,  sinking 
fund,  and  interest  on  all  borrowed  capital)  do  not  exceed  five  (5)  per  cent 
of  the  said  total  cost,  the  project  is  not  attractive;  if  it  be  as  high  as  ten 
(10)  per  cent,  the  enterprise  is  deemed  ordinarily  good;  and  if  it  be  fifteen 
(15)  per  cent  or  more  the  scheme  is  termed  "gilt-edged".  Small  projects 
necessitate  greater  probable  percentages  of  net  earnings  than  do  large 
ones;  and  any  possibility  of  a  future  reduction  of  income  will  call  for  a  high 
estimate  of  net  earning  capacity.  Finally,  the  measure  of  individual 
greed  on  the  part  of  the  investor  will  be  found  to  be  an  important  factor 
in  the  determination  of  the  attractiveness  of  any  suggested  enterprise. 

Such  investigations  as  the  economics  of  an  important  project  should 
generally  be  entrusted  only  to  engineers  experienced  in  the  line  of  activity 
to  which  the  said  project  properly  belongs;  for  if  they  be  left  to  inexper- 
ienced investigators,  it  is  more  than  likely  that  mistakes  will  be  made  and 
money  lost  in  consequence.  The  professional  men  who  generally  do  such 
work  are  the  independent  consulting  engineers;  certain  specialists  retained 
on  salary  solely  for  this  purpose  by  important  organizations,  such  as  rail- 
road companies;  and  engineers  who  are  regularly  in  the  employ  of  large 
banking  houses.  The  work  involved  is  of  such  importance  that  it  usually 
commands  large  compensation — as,  indeed,  it  should;  because  to  do  it 
effectively  demands  not  only  long  experience  but  also  good  judgment  and 
a  vast  amount  of  mental  labor,  both  in  order  to  make  oneself  capable  in 
general  and  so  as  to  consider  thoroughly  all  the  points  embraced  by  the 
special  problem  in  hand. 

This  fundamental  economic  problem  is  often  one  of  extreme  com  plica- 


tion,  involving,  perhaps,  a  determination  of  the  character  of  the  proposed 
improvement,  a  choice  of  sites  or  routes,  a  selection  of  uses,  a  considera- 
tion of  aesthetics,  an  option  on  type  or  style  of  construction,  a  question  of 
ultimate  durability,  a  study  of  greatest  possible  convenience,  a  prevision 
of  serious  opposition,  a  prognostication  of  future  conditions,  an  anticipa- 
tion of  prospective  structural  modifications,  and  a  safe  estimate  of  cost. 
The  best  way  to  illustrate  such  complication  is  by  presenting  a  few  exam- 
ples of  actual  cases,  either  pending  or  already  solved;  and  in  so  doing  the 
speaker  hopes  that  he  will  be  pardoned  for  selecting  them  mainly  from 
his  own  specialty  of  bridgework  and  his  own  personal  experience,  because 
he  can  thus  enter  more  fully  into  detail  and  can  vouch  for  the  information's 
being  correct. 

CASE  I 

There  is  in  contemplation  a  project  for  building  a  long,  high,  and  ex- 
ceedingly expensive  bridge  across  San  Francisco  Harbor  so  as  to  connect 
the  great  city  of  San  Francisco  with  the  cities  of  Oakland,  Berkeley,  and 
its  other  suburbs.  This  project  has  been  a  dream  for  at  least  a  decade; 
but  it  is  not  a  pipe-dream,  because  some  day  in  some  manner  or  other  it 
is  certain  to  be  realized.  Some  eight  years  ago  the  speaker  prepared  a 
report  for  a  banker  on  the  feasibility  of  the  project,  the  necessity  for  the 
structure,  the  possible  revenue  from  its  use,  and  its  approximate  cost; 
and  since  then  several  other  engineers  have  made  independent  studies  of 
the  problem.  The  communities  interested,  however,  have  taken  as  yet 
no  sensible  step  towards  making  a  thorough  study  of  the  question. 

How  short  sighted  most  promoters  of  important  projects  can  be!  They 
imagine  they  can  obtain  expert  opinion  of  real  value  without  paying  for 
it;  consequently  they  collect  a  mass  of  scattered  and  divergent  information, 
which,  in  most  cases,  is  of  no  earthly  use.  Any  project  of  importance  is, 
of  necessity,  a  great  economic  problem,  and  ought  to  be  solved  at  the  very 
outset  by  special  engineering  talent  of  the  highest  order. 

A  glaring  example  of  the  utter  folly  of  a  community  in  proceeding  with 
important  engineering  construction  without  first  having  a  thorough 
economic  study  of  the  problem  made  by  a  competent  specialist  is  given 
in  Engineering  News  of  November  30,  1916.  It  relates  to  the  municipal 
water-power  enterprise  on  which  the  city  of  Montreal  has  been  busy  for 
some  years.  Feeling  that  the  work  was  being  sadly  mismanaged,  certain 
prominent  Canadian  engineers  "butted  in",  investigated,  and  reported 
upon  the  incomplete  project.  They  showed  that  the  $12,000,000  enter- 
prise which  the  city  had  about  half  finished  will  fall  so  far  short  of  returning 
a  profit  on  its  cost,  and  that  it  has  so  many  serious  defects,  that  it  will  be 
far  better  for  the  community  to  lose  all  it  has  thus  far  expended  than  to 
incur  the  additional  outlay  necessary  to  complete  the  work.  A  thorough 
investigation  to  determine  beforehand  whether  the  scheme  would  be  profit- 
able would  certainly  have  indicated  the  futility  of  constructing  on  the 
lines  that  were  adopted. 

But  to  return  to  the  case  of  the  proposed  San  Francisco  Harbor  bridge — 
practically  none  of  the  governing  conditions  are  satisfactorily  known; 
and,  judging  by  present  indications,  it  is  likely  to  be  a  long  time  before 


they  will  be,  unless,  perchance,  the  leading  citizens  of  the  various  commu- 
nities concerned  bestir  themselves  and  prevail  on  their  ruling  bodies  to 
join  forces,  raise  the  requisite  funds,  choose  an  engineer  of  national  repu- 
tation (or,  preferably,  a  board  of  three  such  engineers),  arrange  to  allow 
him  or  them  adequate  compensation  for  expert  services  and  all  the  money 
necessary  for  borings  and  other  investigations,  accord  ample  time  for  the 
entire  work,  and  thus  obtain  a  report  that  will  settle  finally  all  the  import- 
ant economic  and  technical  points  involved  in  the  proposition. 

The  main  features  to  determine  are  as  follows,  the  listing  being  done 
according  to  relative  importance: 

FIRST.  The  probable  gross  incomes  from  all  practicabl  •  combinations 
of  the  various  sources,  year  by  year  for  a  long  term  of  years,  and  the  pro- 
portion thereof  that  is  likely  to  prove  net  in  each  combination. 

SECOND.  Based  upon  the  result  of  this  investigation,  the  determina- 
tion of  the  extreme  superior  limit  of  cost  for  the  structure  for  each  combi- 
nation of  the  different  kinds  of  traffic. 

THIRD.  In  view  of  the  great  depths  of  water  in  the  harbor,  what  one 
or  more  of  the  several  proposed  or  possible  sites  might  be  utilized  for 
building  a  bridge  within  the  several  ascertained  limits  of  cost. 

FOURTH.  Of  what  kind  of  traffic  it  is  advisable  that  the  proposed 
bridge  should  take  care. 

FIFTH.  The  character  of  the  foundation  soil  as  determined  beyond  all 
doubt  by  making  proper  borings,  and  the  settlement  of  best  depths  for 
all  pier  foundations. 

SIXTH.  The  various  requirements  of  the  U.  S.  Government  in  respect 
to  minimum  span-lengths,  vertical  clearances,  and  temporary  obstruction 
of  waterway  for  each  proposed  crossing. 

SEVENTH.  The  minimum  clear  headway  which,  for  a  combination  of 
all  reasons,  it  is  expedient  to  adopt  for  each  proposed  crossing;  and  the 
choice  between  a  bridge  with  and  a  bridge  without  an  opening  span  or 
opening  spans. 

EIGHTH.  A  safe  estimate  of  total  cost  of  structure  for  each  layout 
that  proves  to  be  feasible,  and  the  corresponding  estimates  of  cost  of 
operation,  maintenance,  repairs,  etc. 

NINTH.  The  time  required  for  completion  of  construction  of  the 
structure  for  each  feasible  layout. 

After  all  these  points  have  been  settled  and  embodied  in  a  report,  it 
will  be  easy  to  determine  finally  whether,  either  at  the  present  time  or 
within  a  certain  number  of  years,  it  will  be  feasible  or  advisable  to  build 
the  proposed  structure;  where  it  should  be  located;  what  traffic  it  should 
carry;  how  long  it  will  take  to  build  it;  what  it  will  cost  for  construction, 
maintenance,  and  operation;  and  how  the  necessary  funds  are  to  be 
provided. 

The  actual  conditions  for  the  proposed  San  Francisco  Harbor  bridge, 
as  well  as  they  can  be  stated  at  present,  are  as  follows: 

A.  There  is  a  large  possible  income  from  passenger  traffic,  mainly 
from  commuters  who  now  use  the  ferry,  most  of  which  traffic  would  soon 
be  diverted  to  the  structure,  provided  that  truly-rapid  transit  thereon 


be  furnished  at  all  times;  and  the  said  income,  under  present  conditions, 
would  be  large  enough  to  warrant  the  building  of  an  open-decked,  double- 
track,  electric-railway  bridge  which  would  carry  no  other  kind  of  traffic. 

B.  There  is  a  rapidly  increasing  amount  of  automobile  traffic  now  cared 
for  by  the  ferry;  and  this,  undoubtedly,  would  be  augmented  materially 
by  the  superior  and,  possibly,  cheaper  service  of  the  bridge;  nevertheless 
it  is  doubtful  whether  it  would  be  large  enough  to  warrant  the  building 
of  separate  passageways  with  paved  floor  and  the  necessarily  greater 
carrying  capacity  of  the  trusses.    It  would  be  out  of  the  question  to  let 
the  automobiles  use  the  same  space  as  the  electric  trains;  for  such  an 
arrangement  would  prevent  the  rapid  transit  of  the  latter. 

C.  There  is  an  immense  amount  of  freight  crossing  the  water;  but, 
for  two  reasons,  it  does  not  appear  probable  that  it  would  ever  be  econom- 
ical to  transport  it  over  a  bridge.    The  first  reason  is  the  great  height  to 
which  both  it  and  its  containing  vehicles  would  have  to  be  lifted,  and  the 
consequent  expense  of  such  lifting.    The  second  is  the  greatly  augmented 
cost  of  structure,  due  to  the  far  larger  live  loads  for  both  the  floor  system 
and  the  trusses,  that  the  carrying  of  such  freight  would  necessitate.    It 
would  probably  be  more  economical  either  to  transfer  the  freight  by  ferry 
as  is  done  at  present,  or  to  carry  it  by  rail  around  the  south  end  of  the  Bay. 

D.  There  is  at  certain  seasons  a  large  amount  of  passenger  traffic  to 
and  from  San  Francisco  by  certain  trans-continental  railroads;  hence  the 
question  arises  whether  the  passengers  should  be  carried  across  in  the 
steam-railway  cars  on  which  they  travel  or  whether  they  should  go  over 
in  the  electric-railway  cars.    The  objection  to  the  latter  method  is  the 
individual  trouble,  inconvenience,  and  loss  of  time  for  each  passenger; 
while  the  objection  to  the  former  is  the  increased  cost  of  structure  due  to 
the  difference  in  the  live  loads  between  steam-railway  cars  and  electric- 
railway  cars.    Of  course,  the  former  would  have  to  be  hauled  in  short 
trains  by  electric  motors  so  as  to  avoid  the  excessive  concentrated  loading 
from  the  heavy  steam-locomotives. 

E.  The  most  direct  route  for  the  crossing  is  from  Telegraph  Hill  to  the 
outer  end  of  Goat  Island,  and  thence  to  near  the  Oakland  Pier;  and  this 
is  the  one  to  which,  until  quite  lately,  most  attention  has  been  paid.    The 
main  objections  to  it  are  as  follows: 

FIRST.  The  depth  of  water  between  the  city  and  Goat  Island  is  ex- 
cessive, thus  making  the  pier  foundations  very  expensive. 

SECOND.  A  large  proportion  of  the  steamers  using  the  harbor  would 
have  to  pass  under  the  structure. 

THIRD.  The  War-Department  requirements  in  respect  to  both  hori- 
zontal and  vertical  clearances  would  be  excessive  for  this  location  because 
of  the  large  number  of  vessels  passing;  and,  in  consequence,  the  cost  of 
structure  would  be  greatly  augmented. 

F.  By  locating  further  inside  the  Bay,  the  depth  of  water  would  be 
reduced  to  a  reasonable  amount,  and  the  number  of  vessels  passing  the 
structure  would  be  comparatively  small.    In  fact,  the  farther  back  from 
the  harbor-entrance  the  structure  is  located,  the  smaller  will  be  the  depth 
of  water  and  the  fewer  will  be  the  passing  vessels.    On  the  other  hand, 

8 


though,  the  greater  will  be  the  total  length  of  structure,  the  farther  from 
the  centre  of  population  will  be  its  city  end,  and  the  greater  will  be  the 
distance  which  the  passengers  will  have  to  travel. 

G.  Practically  nothing  is  known  about  the  characters  of  foundations 
that  would  be  encountered  at  the  various  proposed  locations;  and  no  pro- 
vision has  been  made  for  money  to  make  the  necessary  borings. 

H.  It  is  impracticable  to  obtain  a  final  decision  concerning  required 
span-lengths  until  a  bonafide  design,  properly  backed,  has  been  presented 
to  the  War  Department  for  approval. 

I.  In  regard  to  minimum  clear-headway,  it  is  probable  that  the  farther 
inside  the  harbor  the  location  the  less  the  requirement,  because  the 
smaller  and  less  important  would  be  the  passing  craft,  and  the  fewer  the 
number  thereof.  Some  of  them  might  be  forced  to  lower  topgallant 
masts  in  order  to  pass  beneath  the  structure. 

J.  There  would  be  a  serious  objection  to  any  opening  span  because 
of  the  delay  which  would  be  involved  by  its  operation.  The  real  raison 
d'etre  of  the  structure  is  rapid  transit,  hence  to  interfere  with  it  in  any 
way  would  be  highly  objectionable. 

K.  The  total  cost  of  structure  would  decrease  to  a  certain  point  as 
the  location  is  moved  up  the  harbor,  because  of  cheaper  foundations  and 
the  consequently  shorter  spans;  but  beyond  the  said  point  it  would  in- 
crease because  of  the  greater  length  of  bridge. 

L.  The  more  expensive  the  structure  the  longer  will  be  the  time  re- 
quired to  build  it;  hence  it  may  be  concluded  that  one  of  the  inner  harbor 
locations  would  need  much  less  time  for  completion  of  bridge  than  the 
Goat-Island  layout.  This  matter  of  time  for  completion  of  structure 
possesses  a  double  importance,  because  any  delay  increases  the  item  of 
cost  due  to  interest  during  construction;  and  by  postponing  the  inception 
of  operation  it  involves  a  loss  of  income  from  use. 

From  the  preceding  it  is  evident  that  the  solution  of  the  initial  economic 
problem  in  connection  with  the  proposed  San  Francisco  Harbor  bridge 
is  one  of  considerable  complication. 

CASE  II 

The  City  of  New  Orleans  for  many  years  has  had  under  consideration 
the  building  of  a  combined  railway  and  highway  bridge  across  the  Missis- 
sippi River;  and  within  the  last  year  the  project  has  been  seriously  con- 
templated. 

Nearly  two  decades  ago  the  late  Collis  P.  Huntington,  President  of  the 
Southern  Pacific  Railway  Company,  and  his  consulting  engineer,  the  late 
Dr.  Elmer  L.  Corthell,  made  an  investigation  of  the  scheme  of  building 
at  that  place  a  double-track  railway  bridge;  and  they  called  in  as  advisory 
engineers  the  speaker  and  his  brother,  Montgomery,  to  estimate  upon  the 
cost  of  a  low  bridge.  The  death  of  Mr.  Huntington,  which  occurred 
shortly  afterwards,  caused  the  project  to  be  dropped;  and  it  was  never 
revived.  The  speaker's  study  was  made  with  considerable  thoroughness. 
It  involved  the  solution  of  two  or  three  problems  of  great  magnitude 
which  were  new  to  the  engineering  profession,  the  principal  economic  one 

9 


being  a  comparison  of  costs  of  a  high  bridge  and  a  low  bridge.  The  result 
was  decidedly  in  favor  of  the  latter. 

The  problem  now  facing  the  City,  however,  is  much  more  complicated, 
involving,  as  it  does,  a  combination  of  steam-railway,  electric-railway, 
vehicular,  and  pedestrian  traffics.  There  is  a  choice  between  two  locations, 
one  near  the  centre  of  the  city  and  the  other  several  miles  further  up- 
stream— in  fact,  some  intermediate  locations  might  have  to  be  considered. 
There  is  a  sentiment  among  certain  prominent  citizens  favoring  a  tunnel 
rather  than  a  bridge;  and,  on  that  account,  the  question  of  bridge  versus 
tunnel  will  have  to  be  considered,  notwithstanding  the  fact  that  the  diffi- 
culties presented  by  the  tunnel  proposition  are  almost  insurmountable 
in  view  of  the  present  status  of  engineering  knowledge  and  experience. 

The  question  of  high-bridge  versus  low-bridge  will  have  to  be  thoroughly 
thrashed  out  in  order  to  please  the  populace,  although  any  truly-exper- 
ienced engineer  would  determine  very  quickly  in  favor  of  the  latter, 
irrespective  of  the  possible  opposition  of  the  river  interests  and  even  that 
of  the  War  Department. 

The  economic  method  of  handling  the  combination  of  the  various 
kinds  of  traffic  would  require  some  study  to  determine;  and  the  best 
method  might  vary  with  the  location  of  the  structure. 

The  style  and  dimensions  of  the  moving  span — whether  swing,  bascule, 
or  vertical  lift — and  the  sizes  of  the  clear  opening  or  openings  are  mooted 
points  involving  a  consideration  of  economics  and  other  important  matters. 
This  question  is  complicated  by  the  fact  that  the  requirements  ought  to 
be  dependent  on  the  location;  because  at  the  upper  one  there  would  be 
very  few  vessels  passing,  while  at  the  lower  one  there  would  be  many. 

The  unprecedented  depth  for  the  pier  foundations  involves  an  economic 
study  in  order  to  ascertain  the  best  method  of  sinking  and  founding. 

The  facilities  for  freight,  passenger,  and  vehicular  traffic  afforded  by 
the  several  proposed  crossings  would  affect  the  total  earnings  of  the  struc- 
ture; hence  this  feature  should  receive  special  attention. 

The  grade  and  alignment  for  any  proposed  crossing  are  factors  that 
must  be  included  in  the  economic  study,  because  they  affect  the  cost  of 
handling  the  traffic;  and  the  matter  of  right-of-way  may  prove  an  import- 
ant consideration. 

The  property  damages  involved  by  the  approaches  to  the  structure  and 
the  shifting  of  existing  tracks  would  differ  materially  in  cost  at  the  various 
possible  crossings,  hence  this  feature  is  one  involving  economics. 

The  choice  between  single-deck  and  double-deck  spans  entails  a  con- 
sideration of  economics  that  may  prove  to  be  of  some  importance. 

After  determining  the  various  kinds  of  traffic  to  take  care  of,  there 
remains  the  economic  problem  of  deciding  upon  the  live  loads  for  the 
various  parts  of  the  structure.  If  these  are  made  too  high,  there  is  a 
waste  of  material  involved,  and  the  bridge  enterprise  will  forever  after  be 
burdened  with  an  unnecessarily  large  annual  interest  to  be  paid  on  that 
account;  but  if  they  are  made  much  too  low,  the  life  of  the  structure  will  be 
curtailed.  The  saving  clause,  however,  in  respect  to  this  adjustment  is 
that,  ordinarily,  a  steel  bridge  does  not  have  to  be  removed  because  of 

10 


overloading  until  the  metal  thereof  is  actually  stressed  at  least  fifty  (50) 
per  cent  more  than  the  permissible  intensities  of  working  stresses  given 
in  standard  specifications  for  design. 

This  general  problem  of  the  proposed  New  Orleans  bridge,  while  not 
so  complicated  as  that  of  the  proposed  San  Francisco-Harbor  structure, 
is  of  an  intricate  nature,  and  will  demand  for  its  solution  engineering 
ability  and  experience  of  the  highest  order. 

CASE  III 

There  is  given  in  the  speaker's  treatise  on  "Bridge  Engineering"  in 
the  Chapter  on  "Reports",  on  pp.  1575  to  1581,  inclusive,  an  economic 
study  for  the  replacement  of  a  bridge  over  the  Mississippi  River,  which 
illustrates  some  of  the  economic  questions  that  arise  in  a  consulting  bridge 
engineer's  practice.  In  that  case  the  point  at  issue  was  whether  it  would  be 
best  to  build  a  single-track  or  a  double-track  bridge  or  to  arrange  for  the 
conversion  at  some  future  time  of  a  single-track  structure  into  a  double- 
track  one.  Five  methods  of  doing  the  latter  were  suggested,  and  the  esti- 
mates of  their  total  first  cost  were  made;  then,  at  an  assumed  rate  of  in- 
terest, a  table  was  prepared  showing  the  total  cost  of  each  structure  plus 
interest  thereon  for  periods  of  five  years,  up  to  the  limit  of  forty  years. 
That  table  indicates  at  a  glance  the  comparative  economics  of  all  five 
methods  at  any  of  the  five-year  periods.  A  diagram  prepared  from  the 
said  table,  of  course,  would  be  preferable,  as  it  would  show  more  readily 
the  comparison  at  any  intermediate  period. 

CASE  IV 

As  stated  by  Lavis,  "The  application  of  economics  to  railroad  location 
and  construction  consists  in  the  proper  adjustment  and  balance  between 
the  first  cost  as  exemplified  by  the  straight  line  of  uniform  rate  of  gradient 
and  the  first  cost  of  a  line  or  a  series  of  lines  which  deviates  from  it  in 
more  or  less  degree,  and  the  difference  in  cost  of  operation  due  to  this 
deviation  (whether  lateral  or  vertical),  and  the  consequent  introduction 
of  added  resistance  and,  therefore,  added  cost  of  operation".  In  railroad 
engineering  there  are,  certainly,  quite  complicated  preliminary  economic 
problems  to  solve,  among  which  may  be  mentioned  the  following: 

A.  A  location  of  the  road  which  will  ensure  that  the  net  earnings  shall 
be  as  large  as  possible;  and  to  do  this  it  will  be  necessary  to  run  the  line 
to  or  through  all  important  traffic-points  which  can  reasonably  be  reached. 

B.  An  adjustment  between  the  character  of  the  construction  and  the 
probable  gross  income  from  traffic.    If  the  latter  be  large,  it  will  pay  to 
build  a  first-class  road  with  heavy  rails,  light  grades,  easy  curves,  com- 
paratively expensive  station  buildings,  and  permanent  structures;  but  if 
it  be  small,  the  original  rails  may  be  light,  the  grades  comparatively 
heavy,  the  curves  rather  sharp,  the  station  buildings  cheap,  and  the 
structures  temporary. 

C.  An  adjustment  between  the  total  length  of  line  between  termini 
and  the  amount  of  money  available  for  construction.    Under  ordinary 
conditions  and  within  certain  limits,  a  railway  line  can  often  be  cheapened 
by  lengthening  it.    This,  of  course,  is  done  by  increasing  the  total  amount 

11 


of  curvature,  and,  consequently,  the  cost  of  operation.  Holbrook  states 
that  for  each  degree  of  curvature  there  is  an  added  train-resistance 
equivalent  to  a  lift  of  four  or  five  hundredths  of  a  foot,  so  that  a  complete 
circular  curvature  is  equivalent  to  a  lift  of  about  sixteen  feet,  or  to  a  haul 
of  one  mile  on  straight,  level  track.  The  energy  required  to  overcome  the 
resistance  to  curvature  is  furnished  by  the  engine;  and  the  work  performed 
by  the  said  energy  is  the  destruction  of  both  the  equipment  and  the  track. 
It  is  difficult  to  determine  the  amount  of  wear  of  wheels  due  to  curvature, 
as  apart  from  that  due  to  straight  line;  but  it  is  not  so  difficult  to  locate 
the  extra  wear  on  the  rails.  From  the  investigations  which  have  been 
made  on  this  subject,  it  has  been  found  that  the  cost  of  repairs  for  the 
damage  done  is  as  great  as  the  cost  of  the  energy  expended  by  the  engine  in 
doing  it,  so  that  the  total  cost  of  curvature,  from  an  operating  standpoint, 
is  at  least  twice  as  great  as  the  cost  of  the  energy  necessary  to  overcome 
the  added  resistance  due  thereto. 

Apropos  of  rail-wear,  it  is  pertinent  to  call  attention  to  the  ultra-con- 
servatism of  most  American  railroad  authorities  in  adhering  to  the  use  of 
rails  that  have  their  webs  perpendicular  to  the  upper  faces  of  the  ties 
instead  of  perpendicular  to  the  coned  faces  of  the  wheels.  This  divergence 
from  the  normal,  which  is  only  one  in  twenty,  can  best  be  secured  by  using 
beveled  tie-plates.  The  effect  of  it  on  tangent  is  to  reduce  the  rotating 
bending-moment  on  the  rail  to  zero  and  to  bring  the  wear  on  both  rails 
and  wheels  to  a  minimum,  also  to  make  the  said  wear  regular,  uniform, 
and  parallel  to  the  top  normal  plane  of  the  rails  and  to  the  coned  surfaces 
of  the  wheels.  In  turn,  this  effect  makes  the  trucks  ride  more  easily  and 
smoothly,  and  thus  reduces  the  rack  on  the  locomotives  and  cars. 

Again,  many  railroad  officials  object  to  the  widening  of  gauge  on  curves, 
in  spite  of  the  glaringly-evident  fact  that,  unless  this  be  done,  the  rigid 
trucks  will  cause  the  wheels  to  grind  against  the  inner  faces  of  the  rail- 
heads. The  necessity  for  this  widening  is  so  obvious  that  the  speaker 
cannot  comprehend  the  obstinacy  of  any  railroad  man  in  adhering  to  the 
maintenance  of  a  constant  gauge  for  both  tangents  and  curves.  Nor  can 
he  appreciate  the  reasoning  of  those  who  refuse  to  incline  the  rail-webs 
so  as  to  be  normal  to  the  wheel-coning.  Both  of  these  changes  in  American 
current  practice  are  so  obviously  beneficial  that  any  scientifically-thinking 
man  must  concede  their  desirability. 

Returning  to  the  matter  of  curvature,  there  are  other  somewhat  intan- 
gible factors  which  enter  into  its  cost-effect — principally  those  due  to  the 
limited  field  of  view  on  curves.  An  examination  into  the  cause  of  wrecks 
and  of  injury  and  death  to  trackmen  and  others  on  the  track  discloses  the 
fact  that  most  of  these  would  not  have  happened,  had  there  not  been  a 
curve  in  the  vicinity.  The  extra  strain  upon  the  track  and  the  equipment 
due  to  curves  also  leads  to  accidents  which  would  not  otherwise  occur. 

It  is  evident,  therefore,  that  this  particular  economic  problem  involves 
not  merely  first-cost  of  construction  but  also  cost  of  operation. 

D.  A  proper  determination  of  the  ruling  grade  in  reference  to  both  the 
present  and  the  prospective  traffic.  By  reducing  the  ruling  grade  we  make 
it  possible  to  handle  heavier  trains;  and,  therefore,  fewer  trains  are  neces- 

12 


sary.    This  results  in  a  saving  (possibly  a  very  large  one)  in  the  operating 
expenses. 

E.  An  adjustment  between  the  total  rise  and  fall  of  grades  and  the 
first  cost  of  grading.    Of  course,  the  maximum  height  to  be  surmounted 
can  very  seldom  be  controlled  to  any  appreciable  extent,  unless  resort  be 
made  to  tunnelling  in  the  vicinity  of  the  summit;  but  the  minor  apices  and 
depressions  can  be  reduced  by  increasing  the  quantities  in  the  cuts  and 
fills.    As  in  the  last  case,  this  economic  feature  is  by  no  means  one  of  first 
cost  only,  because  the  total  amount  of  rise  and  the  cost  of  energy  expended 
increase  and  decrease  together.    Although  it  is  true  that  some  of  the  energy 
stored  in  the  train  on  a  down  grade  can  be  utilized  for  climbing  the  next 
rise,  the  amount  thereof  is  generally  small. 

F.  The  time  allowed  for  completing  the  road.     This  is  always  an 
economic  feature  because  of  the  question  of  interest  during  construction. 
The  longer  the  time  required  to  finish  the  line  and  to  put  it  in  operation 
the  greater  .will  be  the  amount  of  the  interest  on  the  capital  borrowed  to 
pay  for  construction;  consequently  it  will  sometimes  be  truly  economical 
to  expend  extra  money  on  first  cost  in  order  to  shorten  the  time  for  com- 
pletion.   There  is  another  economic  feature  that  is  sometimes  involved  by 
the  time  element,  and  which  often  becomes  temporarily  of  paramount 
importance, — viz.,  the  offering  by  communities  of  large  bonuses  in  cash 
or  realty  for  the  finishing  of  the  road  so  as  to  bring  trains  to  certain  places 
at  or  before  certain  times.    Under  such  conditions,  it  often  happens,  and 
very  properly  too,  that  every  nerve  is  stressed  to  the  highest  tension  in 
order  to  accomplish  the  desired  purpose,  regardless  of  the  amount  of  ex- 
penditure of  money  and  effort. 

CASE  V 

In  1914  there  was  prepared  (but  never  published)  by  Robert  C.  Bar- 
nett,  Esq.,  consulting  engineer,  and  now  associate  engineer  in  the  speaker's 
firm,  a  paper  entitled  "A  Comprehensive  Policy  for  River  Improvement". 
This  essay  is  a  masterpiece  of  engineering  economics;  and  as  it  relates  to 
generalities  rather  than  to  details,  it  is  reproduced  here  nearly  verbatim, 
as  follows,  with  the  kind  permission  of  its  writer: 

The  need  for  a  broad,  comprehensive  policy  in  dealing  with  our  rivers 
is  again  forced  home  on  us  by  the  recent  reports  of  the  Army  Engineers, 
the  Geological  Survey,  and  several  private  engineering  firms.  These 
reports,  emanating  from  different  sources  and  inspired  by  different  view 
points,  serve  to  emphasize  the  existing  lack  of  correlation  of  purpose,  of 
coordination  of  plan,  of  cooperation  in  execution. 

We  have  today  various  separated  and  unrelated  organizations  striving 
to  promote  some  form  or  other  of  river  improvement.  For  example, 
there  are  the  Board  of  Army  Engineers,  the  National  Rivers  and  Harbors 
Congress,  the  Geological  Survey,  the  Mississippi  River  Commission,  the 
Mississippi  River  Levee  Association,  the  National  Drainage  Congress,  the 
Interstate  Levee  Association,  and  others.  There  is  no  correlation  of  pur- 
pose— no  coordination  of  effort;  but  each  organization  is  seeing  only  its 
own  special  problem  and  is  overlooking  the  big  fundamental  problem 
underlying  the  whole  subject.  There  is  so  much  at  stake,  so  many  in- 

13 


terests  are  affected,  such  large  investments  are  called  for,  such  far  reaching 
economic  benefits  are  possible,  that  it  is  well  worth  our  while  to  pause  and 
consider  what  this  fundamental  problem  is.  By  such  consideration  we 
shall  come  to  a  better  realization  of  what  we  might  attain;  of  the  inade- 
quacy of  our  present  system  and  methods;  of  the  inefficiency  of  the  many 
detached  and  unrelated  organizations  now  promoting  river  improvements; 
and  of  the  great  need  for  a  policy  broad  enough,  fundamental  enough,  to 
enable  us  to  accomplish  a  permanent  solution. 

Such  a  policy  must  be  based  on  sound  economics;  for  the  general  problem 
is  essentially  an  economic  one.  What  economic  principle  should  form  the 
basis  of  such  a  policy?  Let  us  consider  a  little  more  in  detail,  and  perhaps 
in  an  elementary  way,  the  first  principles  involved. 

The  economic  problem  underlying  the  improvement  of  our  streams  and 
rivers  is  a  most  fundamental  one.  It  is  but  a  phase  of  the  general  economic 
problem  which  confronts  mankind.  This  problem  reduced  to  its  lowest 
terms  is  that  of  satisfying  human  wants.  A  very  large  part  of  our  activi- 
ties has  this  fundamental  object  in  view.  Obviously,  we  are  directly  and 
seriously  concerned  with  the  satisfying  of  the  maximum  amount  of  want — 
not  only  the  maximum  amount  of  individual  want,  but  of  collective  want; 
for  the  interests  of  the  individual  are  so  inter-related,  inter-laced,  and 
connected,  so  dove-tailed  into  each  other,  that  the  individual's  maximum 
does  not  obtain  until  the  maximum  for  the  social  organism  obtains.  This 
is  a  prerequisite  for  economic  equilibrium. 

Should  our  efforts  fall  short  of  producing  this  maximum  satisfaction, 
there  remains  an  unattained  potential  increment.     This  unattained  in- 
crement, measured  by  the  difference  between  possible  attainment   and 
actual  attainment,  is  an  incentive  for  further  effort  in  the  future  to  disturb 
conditions,  to  re-arrange  relations,  to  re-adjust  conflicting  interests.    Such 
disturbance,  such  re-arrangement,  such  re-adjustment  means  an  undoing 
of  the  things  we  are  doing  today,  a  throwing  away  of  improvements  made 
yesterday,  a  backing  up  and  taking  a  fresh  start,  a  wasting  of  time  and  of 
resources.    Such  an  unattained  increment  produces  a  corresponding  in- 
centive which  is  a  continuous  and  persistent  menace  to  our  stability.    It, 
therefore,  behooves  us,  while  formulating  a  policy  for  any  development, 
to  take  into  consideration  the  kind  and  the  amount  of  development  which 
will  ultimately  produce  this  maximum  satisfaction.    Previous  failure  to 
recognize  this  principle  is  today  causing  us  to  undo,  or  to  do  over,  the 
things  of  yesterday.    Had  yesterday's  planning  been  done  on  a  broader, 
a  more,  comprehensive,  a  more  fundamental  basis,  today's  efforts  would 
have  been  in  harmony  therewith;  and,  instead  of  tearing  out  and  replac- 
ing, we  should  simply  have  to  add  to  our  former  achievements,  and  there- 
by get  the  benefit  of  a  cumulative  process  of  development.     It  is  this 
fundamental  principle  of  producing  a  maximum  satisfaction,  or  its  cor- 
relative maximum  utility,  that  we  should  bear  in  mind  when  approaching 
the  problem  of  establishing  a  general  policy  for  the  improvement  of  our 
rivers  and  streams. 

What  is  this  maximum  utility  which  can  be  produced  by  river  improve- 
ment?   If  we  are  to  formulate  a  policy  based  on  maximum  utility,  we 

14 


must  have  some  conception  of  what  that  maximum  utility  is  and  how  it 
may  be  obtained.  Heretofore,  we  have  been  prone  to  regard  our  rivers 
as  available  only  for  one  or  two  purposes.  One  such  purpose,  discovered 
early  in  the  career  of  mankind,  is  that  of  navigation.  This  continued 
along  for  years,  until  navigation,  which  originally  was  a  mere  incident, 
has  come  to  bo  regarded  as  the  sole  and  primary  purpose  of  our  rivers  and 
streams.  To  such  an  extent  has  this  view  obsessed  the  minds  of  our  leg- 
islative bodies  and  the  official  heads  of  departments  that,  until  recently, 
little  or  no  regard  has  been  given  to  the  other  possible  uses  to  which  our 
river  systems  can  be  put.  Note,  for  instance,  how  the  War  Department 
through  the  Army  Engineers  has  considered  navigation  to  be  the  para- 
mount utility.  These  engineers  have,  in  most  cases,  confined  their  work 
to  improvement  of  the  channel  solely  for  navigation  purposes,  ignoring 
the  adjacent  flood  plains  and  their  need  for  protection.  Note  also  how 
the  power  development  at  Keokuk  was  penalized  to  the  extent  of  $2,000,- 
000  in  order  to  construct  a  lock,  a  dry  dock,  buildings,  and  other  improve- 
ments, while  at  the  same  time  the  benefit  to  navigation  rendered  by  such 
power  installation  is  said  by  river  men  to  be  worth  at  least  $5,000,000. 

THE  PRIMARY  AND  FUNDAMENTAL  PURPOSE  OF  OUR  RIVERS  AND 
STREAMS  is  THAT  OF  DRAINING  THE  WATERSHEDS.  This  purpose  obtained 
long  before  the  advent  of  man,  and  still  continues  to  be  the  essential 
function.  Therefore,  our  first  consideration  should  be  to  increase  the 
efficiency  of  these  drainage  channels  for  their  respective  watersheds. 
Hence  our  comprehensive  policy  should  start  from  this  basis.  To  increase 
the  efficiency  of  a  drainage  channel  is  an  engineering  problem;  and  hence 
it  will  not  be  considered  further  at  this  time.  We  might  note  in  passing 
that  it  will  be  found  that  in  planning  for  an  increased  efficiency  of  drainage 
channel,  we  may  obtain  other  incidental  but  very  desirable  results,  in- 
cluding an  augmented  discharge  capacity. 

As  the  country  becomes  settled  and  land  values  augment  because  of  the 
increasing  density  of  population  and  the  production  of  wealth,  the  pro- 
tection of  river  lands  and  of  the  property  and  lives  of  the  people  living 
thereon  becomes  a  matter  of  great  importance.  The  erosion  of  these  rich, 
fertile,  bottom  lands,  the  destruction  of  crops  and  other  property,  the 
jeopardizing  of  human  life  and  often  the  loss  thereof,  all  contribute  to  a 
far-reaching  loss  which  becomes  a  burden  to  the  rest  of  the  country  as 
well  as  to  the  afflicted  districts;  hence  our  comprehensive  policy  should 
recognize  this  very  important  element  of  the  general  problem.  How  to 
secure  flood  protection  is  purely  an  engineering  question,  and  will  be  passed 
over  for  the  present. 

The  need  for  transportation  becomes  more  urgent  as  the  country  settles 
up  and  as  population  concentrates  at  certain  points.  Water  transporta- 
tion is  more  economic  for  certain  classes  of  freight  than  rail  transportation, 
hence  it  is  to  the  general  interest  of  the  country  to  facilitate  the  former, 
consequently  the  navigability  of  our  rivers  should  receive  consideration 
in  our  comprehensive  policy.  How  to  improve  navigation  is  another 
engineering  problem;  and,  as  such,  it  will  be  passed  over  for  the  present. 

As  the  river  towns  expand  into  large  cities,  the  need  for  a  municipal 
water  supply  becomes  of  corresponding  importance,  and,  hence,  should 

15 


receive  attention  in  the  formulation  of  our  comprehensive  policy.  The 
securing  of  a  water  supply  is  likewise  an  engineering  problem. 

In  certain  arid  and  semi-arid  sections  of  the  country  the  needs  of  irri- 
gation are  paramount;  and,  as  a  matter  of  fact,  in  other  sections  favored 
ordinarily  with  abundant  rainfall  there  may  come  a  drought  at  the  critical 
growing  time,  so  that  irrigation  is  much  needed  even  there.  Hence  our 
comprehensive  policy  must  recognize  the  demand  for  irrigation.  How  to 
provide  and  divert  water  for  irrigation  is  also  an  engineering  problem. 

The  development  of  the  country's  resources  is  making  a  larger  and 
larger  demand  for  cheap  power.  Statistics  show  that  the  utilization  of 
power  has  increased  from  2,346,142  H.  P.  in  1870  to  14,641,544  H.  P.  in 
1905.  This  shows  an  increase  in  the  per  capita  consumption  of  from 
0.060  H.  P.  to  0.177  H.  P.  We  must  be  prepared  for  an  increasing  number 
of  power  installations  to  meet  the  growing  demands  of  an  increasing  pop- 
ulation and  an  increasing  per  capita  consumption.  Many  of  our  rivers 
and  streams  have  power  possibilities;  and  the  utilization  of  these  is  of  the 
greatest  economic  concern  to  the  entire  country,  hence  our  comprehensive 
policy  should  provide  encouragement  for  water  power  development.  The 
actual  planning  for  power  and  the  development  thereof  from  our  rivers 
and  streams  constitute  an  engineering  problem;  and,  therefore,  will  be 
passed  over  for  future  consideration. 

From  the  foregoing,  we  see  that  a  comprehensive  policy  for  river  devel- 
opment seeking  to  obtain  the  maximum  utility  should  provide  for  the 
following: 

(a).     An  efficient  drainage  channel  and  an  increased  discharge  capacity. 

(b).  Protection  from  floods,  together  with  reclamation  of  low  lands, 
drainage,  and  prevention  of  erosion. 

(c).    Improved  navigation  facilities. 

(d).     Municipal  water  supply  and  incidental  storage  of  flood  waters. 

(e).  Irrigation,  with  its  incident  diversion-canals  and  its  storage  of 
flood  waters. 

(f).     Water  power  development  and  its  storage  of  flood  waters. 

While  it  is  recognized  that  each  stream  presents  its  own  special  problem 
and  requires  a  specific  solution  to  meet  actual  conditions,  yet  it  is  readily 
seen  that  should  we  fail  to  plan  for  the  ultimate  development  of  all  its 
utilities,  we  fall  short  by  that  much  of  reaching  a  maximum.  Likewise, 
if  we  develop  one  utility  at  the  expense  of  another,  we  fail  to  reach  the 
maximum.  What  is  needed  is  a  plan  or  program  that  will  permit  of  a 
balanced  development.  A  comprehensive  policy  embracing  these  features 
will  make  it  possible  in  many  cases  to  obtain  a  number  of  them  with  one 
investment. 

For  example,  if  it  be  desired  to  provide  a  more  efficient  drainage  channel 
in  order  to  discharge  floods  for  some  watershed,  it  may  be  found  possible 
to  provide  at  the  same  time  levees  that  will  protect  the  lowlands  from 
overflow  and  also  give  an  increased  efficiency  to  the  channel.  The  matter 
of  bank  protection  and  the  prevention  of  erosion  could  be  taken  care  of  in 
the  same  improvement.  By  the  careful  selection  of  a  suitable  channel- 
cross-section  and  the  maintenance  thereof,  navigation  facilities  could  be 

16 


improved  during  low  water,  and  yet  at  high  water  the  discharge  capacity 
of  the  channel  would  not  be  interfered  with.  If  at  the  same  time  our  plan 
of  development  include  diversion  canals  and  storage  reservoirs,  we  can 
relieve  somewhat  the  peak  of  the  flood-flow  while  storing  up  water  for 
irrigation,  municipal  supply,  or  power  purposes.  Such  an  adjustment  of 
related  interests  and  conditions  could  be  obtained  that  a  maximum 
utility  would  result. 

In  contrast  with  this,  consider  some  of  the  actual  conditions  confront- 
ing us  today.  We  find  cases  where  levees  have  been  built  for  flood  pro- 
tection to  the  detriment  of  the  channel.  That  is  the  levees  on  opposite 
sides  of  the  river  approach  and  recede  from  each  other  over  a  wide  range, 
thereby  forming  an  irregularly  varying  channel-cross-section  of  changing 
area  and  differing  hydraulic  radius  with  a  consequent  variation  in  velocity, 
so  that,  during  floods,  silt  is  being  picked  up  at  one  stretch  of  the  river  and 
deposited  in  another;  and  we  get  the  effect  in  places  of  raising  the  river 
bed  above  the  elevation  of  the  adjoining  bottom  lands.  We  find  cases 
where  dams  and  locks  have  been  built  to  improve  navigation  but  no 
attempt  has  been  made  to  utilize  the  resulting  head  for  power  development. 

Again,  consider  the  case  of  a  constructively  navigable  stream  that  will 
hardly  float  a  motor  boat  a  large  part  of  the  year  and  yet  is  rich  in  power 
possibilities.  Under  our  comprehensive  policy,  power  development 
would  be  encouraged.  The  building  of  one  or  more  dams  would  provide 
slack-water  navigation  for  certain  reaches,  while  at  the  same  time  storing 
water  for  power  purposes.  The  storage  of  flood  waters  and  their  subse- 
quent gradual  release  through  the  power  plant  would  equalize  the  flow 
below  the  dam  so  that  navigation  would  be  greatly  benefited  thereby.  The 
development  of  cheap  power  would  bring  in  its  wake  more  industries,  more 
population,  more  need  for  water  transportation,  and  a  great  building  up  of 
the  community,  all  of  which  leads  towards  the  production  of  maximum 
utility. 

Other  examples  could  readily  be  cited;  but  it  is  believed  that  enough 
has  been  said  to  show  the  possibilities  to  be  obtained  by  the  formulation 
of  a  comprehensive  policy  and  to  indicate  the  economic  basis  upon  which 
such  a  policy  should  rest. 

However,  the  excessive  floods  of  last  spring  have  forced  home  the  urgent 
need  for  protection;  and  in  our  anxiety  to  provide  such  protection  we  are 
apt  to  overlook  the  fact  that  the  protection  problem  is  but  a  phase  of  a 
larger  and  more  fundamental  problem.  Unless  this  fundamental  problem 
of  obtaining  the  maximum  utility  is  kept  before  the  minds  of  our  legisla- 
tors and  departmental  heads,  we  are  apt  to  get  only  a  partial  solution  of 
it  because  of  the  desire  to  provide  immediate  protection  and  relief.  The 
investment  that  we  may  now  make  for  partial  relief  will  very  likely  have 
to  be  discarded  later  on,  unless  it  is  made  with  the  view  of  fitting  into  the 
final  development.  It  would  be  better  and,  in  the  long  run,  more  econom- 
ical to  conform  to  a  comprehensive  plan  looking  toward  ultimate  develop- 
ment, even  though  it  take  years  to  carry  out  such  a  program.  We  should 
have  a  very  material  advantage  in  pursuing  a  definite  general  policy,  such 
that  the  work  done  in  the  early  period  of  development  would  not  have  to 
be  undone  at  some  later  stage  and  a  costly  investment  discarded. 

17 


Under  a  general  comprehensive  policy,  our  work  could  be  planned  in 
such  a  way  that  we  should  continually  be  building  up  and  strengthening 
all  investments  and  improvements.  The  desirability  and  efficiency  of 
such  a  policy  must  be  recognized  by  all  students  of  the  situation. 

How  to  impress  the  great  need  of  such  a  policy  on  the  minds  of  our 
public  men,  legislators,  and  officials  of  various  departments,  on  various 
state  and  local  organizations  now  aiming  at  some  one  detail  in  improve- 
ment, is  the  serious  question. 

It  has  been  seen  that  each  feature  to  be  covered  by  the  general  compre- 
hensive policy  required  for  its  attainment  involves  the  solution  of  an 
engineering  problem.  This  being  the  case,  the  formulation  of  such  a 
general  comprehensive  policy  could  best  be  done  by  engineers  who  are 
experts  in  the  several  lines  involved.  It  is  here  that  our  National  Engi- 
neering Societies  could  perform  a  service  for  the  country  in  general  and 
for  the  profession  at  large  by  appointing  a  joint  committee  to  outline  such 
a  policy  and  a  tentative  program  for  securing  its  adoption  and  execution. 
After  the  joint  committee  had  recommended  for  adoption  a  comprehensive 
policy  embracing  the  idea  of  a  balanced  development  of  our  river  systems 
so  that  a  maximum  utility  would  result,  local  engineering  societies  and 
individual  engineers  could  well  assist  the  National  Societies  by  taking  up 
the  work  of  presenting  such  a  policy  to  their  respective  congressmen. 

As  the  primary  purpose  of  this  communication  is  to  emphasize  the  need 
for  a  comprehensive  policy  and  to  impress  on  the  minds  of  all  engineers 
the  importance  of  the  engineering  profession's  taking  a  hand  in  formulating 
such  a  policy  and  in  outlining  a  skeleton  program,  the  writer  will  only 
attempt  at  this  time  to  mention  briefly  some  salient  features  thereof, 
leaving  for  a  future  article  the  presentation  of  a  more  developed  program. 
It  is  believed  that  the  salient  features  of  such  a  preliminary  program 
should  be  the  following: 

An  act  of  Congress  adopting  the  comprehensive  policy,  to  be  recom- 
mended by  the  Joint  Committee  of  the  National  Engineering  Societies, 
and  providing  for  a  Coordinating  Board  of  Engineers,  the  manner  of  select- 
ing them,  and  their  compensation. 

The  cooperation  of  the  States  with  the  National  Government. 

A  division  of  affected  territory  based  on  watersheds  of  convenient  size. 

The  appointment  by  each  interested  State  of  a  State  Board  of  Engineers 
for  this  particular  work,  and  to  provide  for  their  compensation  by  the 
State. 

Each  State  Board  to  work  out  tentative  plans  for  developing  the 
utilities  .of  its  own  rivers  and  streams. 

Where  a  watershed  embraces  more  than  one  state,  the  several  State 
Boards  interested  to  select  from  their  own  membership  a  member  of  the 
Watershed  Board,  so  that  each  State  would  be  represented  on  the  said 
Watershed  Board. 

The  Watershed  Board  to  harmonize  the  plans  of  the  several  State 
Boards  under  it. 

The  various  Watershed  Boards  to  meet  with  the  Board  of  Army  Engi- 
neers and  Federal  authorities  from  time  to  time  and  cooperate  in  perfect- 
ing plans. 

18 


The  various  Watershed  Boards,  the  Board  of  Army  Engineers,  and  the 
Federal  authorities  to  select  an  even  number  of  members  to  form  the 
Coordinating  Board  of  Engineers,  as  provided  by  act  of  Congress.  These 
members  in  turn  to  select  from  the  country  at  large  an  additional  odd 
number  of  engineers  to  complete  this  Board. 

The  purpose  of  the  Coordinating  Board  should  be  to  perfect  the  details 
of  the  program  for  carrying  out  the  purposes  of  the  general  comprehensive 
policy,  to  harmonize  general  plans  for  execution,  and  to  apportion  the 
expense  of  any  improvement  to  those  interests  receiving  the  benefit  of 
such  improvement,  whether  these  be  individuals,  cities,  counties,  states, 
or  the  general  government. 

While  all  this  seems  like  a  very  large  undertaking,  yet  the  benefits  to 
be  derived  by  it  are  of  the  same  magnitude;  and  they  will  eventually 
justify  such  a  program  and  the  investments  made  in  accordance  therewith. 

The  general  features  of  economics  in  respect  to  the  inception  and  finan- 
cing of  engineering  projects  have  now  been  described  at  some  length  for 
bridges,  railroads,  and  river  improvement;  and  this  treatment  of  the  sub- 
ject should  suffice  for  an  example  of  how  to  handle  the  preliminary  eco- 
nomic questions  in  all  other  lines  of  technical  activity. 

We  can  now  pass  to  the  second  division  of  these  lectures, — viz.,  the 
economics  of  design  and  construction;  and  in  so  doing  it  is  practicable 
to  enter  much  more  into  detail  than  we  have  previously;  but  before  dealing 
with  certain  of  the  numerous  specialties  into  which  engineering  is  divided, 
we  shall  touch  lightly  upon  a  few  general  matters  pertaining  to  the  eco- 
nomics thereof. 

Anticipating  The  Future 

In  all  engineering  work  of  both  designing  and  construction,  true  economy 
necessitates  a  thorough  consideration  of  future  requirements  and  possible 
eventualities,  also  a  provision  for  meeting  the  same.  For  instance,  in 
designing  a  structure  one  should  consider  possible  future  additions  of 
loading  and  how  to  accommodate  them;  and  in  construction  one  should 
anticipate  delays,  floods,  storms,  and  other  possible  difficulties,  and  should 
prepare  his  programme  so  as  to  meet  them  effectively  and  without  any 
unnecessary  expenditure  of  time,  labor,  or  money.  Foresight  of  this  kind 
is  an  important  element  of  success  in  the  career  of  every  engineer. 

Systemi? ation 

Quoting  from  the  speaker's  treatise  on  "Bridge  Engineering",  "The 
systemization  of  all  that  one  does  in  connection  with  his  professional  work 
is  one  of  the  most  important  steps  that  can  be  taken  towards  the  attain- 
ment of  success".  Moreover,  it  is  one  of  the  fundamental  elements  of 
economics  in  all  lines  of  work. 

Time   Versus   Material 

Some  designers  in  their  endeavor  to  save  a  small  amount  of  material 
expend  a  large  amount  of  time,  not  only  of  their  own  but  also  of  other 
people's,  which  time  when  properly  evaluated  is  often  greatly  in  excess 
of  the  cost  of  the  material  saved.  Such  economy  as  this  is  false;  and  its 
practice  is  unscientific. 

19 


Labor  Versus  Material 

Similarly  some  designers  in  an  endeavor  to  cut  down  quantities  in  their 
structures  increase  the  labor  thereon  to  such  an  extent  that  the  material 
saved  is  worth  only  a  small  portion  of  the  value  of  the  extra  labor  expended. 
For  instance,  if  one  were  to  make  a  small  pier  hollow,  the  concrete  thus 
saved  would  not  be  worth  anything  like  as  much  as  the  cost  of  the  forms 
required  to  construct  the  hollow  space. 

Recording  Diagrams 

The  study  of  economics  is  greatly  facilitated  by  the  use  of  diagrams 
that  record  quantities  of  materials,  costs  of  construction,  times  of  opera- 
tion, etc.,  for  varying  conditions.  In  general,  it  may  be  stated  that 
American  engineers  do  not  use  graphics  for  studying  economics  to  the 
extent  which  is  advisable;  and  that  in  this  they  might  learn  something 
from  their  European  brethren. 

Economics  of  Mental  Effort 

Almost  nothing  concerning  this  important  subject  is  taught  in  our 
technical  schools;  and  but  little  is  known  about  it  by  practicing  engineers. 
To  be  a  truly  successful  engineer,  one  has  need  to  study  deeply  the  matter 
of  how  best  and  most  economically  to  utilize  his  mental  forces;  how  to 
accomplish  the  greatest  amount  of  work  with  the  smallest  expenditure  of 
effort;  how  many  hours  of  work  per  day  for  long-continued  labor  will 
effect  the  largest  accomplishment;  to  what  extent  men  in  various  lines  of 
activity  should  take  vacations,  and  how  these  should  be  spent;  what  are 
the  effects  upon  one's  working  capacity  from  the  use  of  liquor  and  tobacco 
in  both  small  and  large  quantities;  etc.  All  these  are  ecomonic  questions 
of  great  importance;  and  they  need  to  be  given  proper  attention  by  every 
engineer  who  aspires  to  efficiency  in  both  himself  and  his  employees. 

Again,  the  development  of  the  faculty  of  concentration  is  an  economic 
consideration  of  much  importance. 

Economics  In  Office  Practice 

There  are  many  conditions  in  ordinary  office  practice  that  are  suscepti- 
ble of  considerable  improvement  from  the  economic  point  of  view — for 
instance,  unnecessary  conversation,  useless  duplication  of  labor,  and  lack 
of  proper  checking;  but  this  matter  is  too  complicated  and  lengthy  to 
warrant  more  than  mere  mention  in  a  lecture  of  this  kind.  The  subject 
will  be  found  very  thoroughly  treated  in  Chapter  LVIII  of  the  before- 
mentioned  treatise  on  "Bridge  Engineering". 

Economics  Of  Manufacture 

This  is  a  subject  of  such  complication  and  extent  that  it  can  merely  be 
mentioned  here;  for  upon  it  a  large  treatise  might  readily  be  written.  It 
will  suffice  to  say  that  the  prime  requisites  are  the  prompt  furnishing  at 
all  times  of  materials  and  tools;  the  keeping  on  hand  of  spare  parts  of 
machinery  which  are  liable  to  breakage  or  wear;  the  proper  upkeep  of  all 
machinery  and  apparatus;  the  systematic  arrangement  for  carrying  work 
through  the  shops,  preferably  always  in  one  direction;  the  avoidance  of 
duplication  of  labor;  the  prevention  of  errors,  and  the  speedy  correction 

20 


of  those  which  unavoidably  occur;  the  development  of  individual  efficiency 
in  all  employees;  the  maintenance  of  a  contented  spirit  among  the  work- 
men; and  the  constant  and  intelligent  supervision  of  all  work. 

Economics  Of  Construction 

This  subject  like  the  one  last  discussed  is  of  great  complication,  and  in 
general  principles  the  two  have  much  in  common.  For  instance,  there 
should  be  prepared  for  each  piece  of  construction  an  elaborate  programme, 
indicating  the  various  steps  to  be  taken  and  how  the  work  should  be 
carried  out.  Diagrams  in  this  connection  are  most  useful.  Again,  there 
should  be  prepared  a  time-schedule  for  the  completion  of  the  various 
divisions  of  the  work;  and  this  should  invariably  be  lived  up  to  when  it  is 


There  should  be  a  pre-arranged  schedule  for  the  furnishing  of  all  mater- 
ials and  supplies;  adequate  means  for  the  transportation  thereof  should  be 
provided;  the  workmen  should  be  well  housed  and  fed;  and  should  be  made 
comfortable  and  contented;  disagreements  between  heads  of  departments 
should  be  prevented;  all  possible  difficulties  should  be  anticipated,  and 
means  should  be  at  hand  to  meet  and  overcome  them;  ample  funds  should 
be  provided  for  paying  promptly  all  bills  for  labor  and  materials;  liquor 
should  be  kept  away  from  the  workmen;  and  strike  organizers  and  other 
troublesome  people  should  be  run  off  the  job. 

All  these  matters  are  directly  concerned  with  the  economics  of  construc- 
tion. 

Labor 

The  scientific  handling  of  labor  is  an  economic  problem  of  the  utmost 
importance,  and  a  treatise  could  well  be  written  on  the  subject.  The 
principal  desideratum  is  to  keep  the  workmen  well,  happy,  and  contented; 
and  the  best  ways  to  do  this  are  to  treat  them  kindly,  make  them  com- 
fortable, feed  and  house  them  well,  amuse  them  in  their  spare  time,  don't 
work  them  too  long  hours,  pay  them  by  piece-work  when  practicable, 
listen  patiently  to  their  complaints,  right  their  wrongs,  see  that  they  are 
well  taken  care  of  when  they  are  ill  or  injured,  and  evolve,  if  possible, 
some  feasible  method  of  sharing  profits  with  them.  On  the  other  hand, 
though,  drive  them  hard  and  continuously  during  working  hours,  insist 
upon  their  putting  in  overtime  when  the  conditions  truly  require  it,  dis- 
charge instantly  all  insubordinate  or  otherwise  troublesome  men,  dis- 
pense quietly  with  the  services  of  all  shirkers,  and  insist  that  everybody 
put  forth  his  best  and  most  intelligent  effort  to  effect  the  maximum  of 
accomplishment  in  the  minimum  of  time. 

Waste 

In  all  lines  of  activity  the  avoidance  of  waste  or  extravagance  and  the 
utilization  of  by-products  are  today  burning  questions;  and  upon  their 
proper  solution  by  American  scientists  will  depend  greatly  the  success 
of  our  country  in  its  commercial  struggle  with  the  nations  of  Europe  and 
Asia.  This  statement  is  just  as  true  concerning  engineering  as  it  is  of  any 
other  activity;  and  it  is  encouraging  to  see  that  a  number  of  our  leading 
technical  institutions  are  inaugurating  research  departments  for  the 

21 


furtherance  of  this  object.     Prominent  among  them  in  this  work,  the 
speaker  is  pleased  to  say,  is  the  University  of  Kansas. 

Efficiency  Experts 

A  very  new  type  of  specialist  in  engineering  is  the  efficiency  expert — 
the  man  who  takes  hold  of  moribund  factories  and  other  decaying  enter- 
prises, studies  them  thoroughly  so  as  to  determine  the  raison  d'etre  for 
their  decline,  evolves  the  proper  remedies  for  their  troubles,  puts  them 
again  upon  their  feet,  and  starts  them  upon  the  high  road  to  success.  It 
is  mainly  in  little  matters,  apparently  of  small  importance,  that  such 
concerns  fail;  and  it  requires  a  high  development  of  unusual  talent  in  an 
engineer  to  become  a  truly  successful  efficiency  expert.  Such  work  as 
his  no  one  can  deny  being  "engineering  economics"  in  the  truest  sense 
of  the  term;  and  the  specialty  is  surely  destined  to  become  more  and  more 
popular  and  important  as  the  years  pass  by. 


LECTURE  II 

Having  completed  the  discussion  of  the  principal  topics  of  a  general 
nature  pertaining  to  the  economics  of  designing  and  construction,  it  is 
now  in  order,  as  previously  explained,  to  take  up  the  various  engineering 
specialties,  concerning  the  economics  of  which  the  speaker  has  been  able 
to  collect  sufficient  data  for  his  purpose;  and  these  will  be  treated  in  alpha- 
betical order.  Fortunately  (or  otherwise)  the  first  of  the  group  is  the  line 
of  engineering  activity  in  which  the  speaker  has  specialized  during  more 
than  three  decades,  and  in  which  his  numerous  writings,  extended  over  a 
long  series  of  years,  deal  at  great  length  with  the  important  subject  of 
economy.  On  that  account,  the  volume  of  data  at  hand  is  unusually 
large;  and  this  is  the  explanation  of  the  fact  that  the  treatment  of  this 
subject  is  much  fuller  in  detail  than  that  of  any  of  the  others.  It  is  hoped 
that  the  speaker  will  be  pardoned  for  making  numerous  and  somewhat 
lengthy  quotations  from  his  latest  treatise,  as  it  was  issued  only  last 
summer,  and  as  he  cannot  well  improve  upon  what  he  has  said  therein 
upon  the  subject  of  "True  Economy  in  Design". 

The  great  majority  of  bridge  designers  believe  that  the  most  economic 
structure  is  the  one  for  which  the  first  cost  is  a  minimum;  and  from  the 
contractor's  prejudiced  point  of  view  this  is  correct,  because  his  interest 
generally  lies  in  securing  the  contract  for  the  work  regardless  of  all  other 
considerations  than  his  own  profit;  but  from  the  purchaser's  point  of  view 
that  structure  is  the  most  economic  which  will  do  the  work  required  of  it 
for  as  long  a  time  as  necessary  with  the  least  possible  expenditure  for 
operation,  maintenance,  and  repairs,  all  these  desiderata  being  obtained 
with  the  smallest  practicable  initial  cost  of  construction. 

Treatise  after  treatise  has  been  written  upon  the  subject  of  economy  in 
superstructure  design,  but  unfortunately  the  result  is  simply  a  waste  of 
good  mental  energy;  for  the  writers  thereof  invariably  attack  the  problem 
by  means  of  complicated  mathematical  investigations,  not  recognizing 

22 


the  fact  that  the  questions  they  endeavor  to  solve  are  altogether  too  in- 
tricate to  be  undertaken  by  mathematics.  The  object  of  each  investiga- 
tion appears  to  have  been  to  establish  an  equation  for  the  economic  depth 
of  truss,  or  that  depth  which  corresponds  to  the  minimum  amount  of 
metal  required  for  the  said  truss;  and,  to  start  the  investigation,  it  seems 
to  have  been  customary  to  make  certain  assumptions  which  are  not  even 
approximately  correct.  For  instance,  the  principal  assumption  of  several 
treatises  in  French  and  English  is  that  the  sectional  area  and  the  weight 
of  each  member  of  a  truss  are  directly  proportional  to  its  greatest  stress; 
or,  in  other  words,  that  in  proportioning  all  members  of  trusses  a  constant 
intensity  of  working  stress  is  to  be  used,  while  in  reality  for  modern  steel 
bridges  the  intensities  often  vary  considerably  in  the  same  specifications. 
Again,  no  distinction  is  made  between  tension  and  compression  members, 
and  no  account  is  taken  of  the  greatly  varying  amounts  of  their  percent- 
ages of  weights  of  details. 

There  is,  however,  one  mathematical  investigation  concerning  eco- 
nomic truss  depths  which  is  approximately  correct,  and  which  is  based 
on  assumptions  that  arc  very  nearly  true;  but  it  holds  good  only  for 
trusses  with  parallel  chords,  for  which  structures  it  shows  that  the  greatest 
ecomony  of  material  will  prevail  when  the  weight  of  the  chords  is  equal  to 
the  weight  of  the  web. 

It  has  been  found  by  experience  that,  for  trusses  with  polygonal  top 
chords,  the  economic  depths,  as  far  as  weight  of  metal  is  concerned,  are 
generally  much  greater  than  certain  important  conditions  will  permit  to 
be  used.  For  instance,  especially  in  single-track,  pin-connected  bridges, 
after  a  certain  truss  depth  is  exceeded,  the  overturning  effect  of  the  wind- 
pressure  is  so  great  as  to  reduce  the  dead-load  tension  on  the  windward 
bottom  chord  to  such  an  extent  that  the  compression  from  the  wind  load 
carried  by  the  lower  lateral  system  causes  reversion  of  stress,  and  such 
reversion  eye-bars  are  not  adapted  to  withstand.  A  very  deep  truss  re- 
quires an  expensive  traveller,  and  decreasing  the  theoretically  economic 
depth  increases  the  weight  but  slightly;  hence  it  is  really  economical  to 
reduce  the  depth  of  both  truss  and  traveller.  Again,  the  total  cost  of  a 
structure  does  not  vary  directly  as  the  total  weight  of  metal,  for  the  reason 
that  an  increase  in  the  sectional  area  of  a  piece  adds  nothing  to  the  cost 
of  its  manufacture,  and  but  little  to  the  cost  of  erection;  consequently 
it  is  only  for  raw  material  and  freight  that  the  expense  is  really  augmented. 
Hence  it  is  generally  best  to  use  truss  depths  considerably  less  than  those 
which  would  require  the  minimum  amount  of  metal.  For  parallel  chords, 
the  theoretically  economic  truss  depths  vary  from  one-fifth  of  the  span 
for  spans  of  100  feet  to  about  one-sixth  of  the  span  for  spans  of  200  feet; 
but  for  modern  single-track-railway  through-bridges  the  least  allowable 
truss  depth  is  about  30  feet,  unless  suspended  floor-beams  be  used,  a  detail 
which  very  properly  has  gone  out  of  fashion. 

In  designing  plate-girders,  if  one  will  adopt  such  a  depth  as  will  make 
the  total  weight  of  the  web  with  its  splice-plates  and  stiffening  angles 
about  equal  to  the  weight  of  the  flanges,  he  will  obtain  an  economically 
designed  girder,  and  a  deep  and  stiff  one.  For  long  spans,  however,  this 
arrangement  would  make  the  girders  so  deep  as  to  become  clumsy  and 

23 


expensive  to  handle;  consequently,  when  a  span  exceeds  about  forty  feet, 
the  amount  of  metal  in  the  flanges  should  be  a  little  greater  than  that  in 
the  web;  and  the  more  the  span  exceeds  forty  feet  the  greater  should  be 
the  relative  amount  of  metal  in  the  flanges. 

A  rather  lengthy  mathematical  investigation  for  plate-girders,  based 
upon  fairly  accurate  assumptions,  proves  that  the  theoretical  maximum 
of  economy  exists  when  the  gross  areas  of  flanges  and  of  web  at  mid-span 
are  equal — a  condition  readily  remembered.  Although  this  is  the  theoret- 
ically correct  criterion  for  economy,  if  it  be  applied  to  any  particular  case, 
it  will  generally  be  found  that  the  resulting  web  depth  is  so  excessive  as 
to  cause  one  or  more  of  the  following  modifications  in  construction,  as 
compared  with  the  depth  which  would  make  the  total  weight  of  the  flanges 
equal  to  the  total  weight  of  the  web  with  all  its  details: 

A.  An  additional  splice  or  two  in  the  web,  or  else  a  slightly  increased 
pound  price  for  the  large  plates. 

B.  Larger  outstanding  legs  for  all  stiffening  angles. 

C.  Reduction  in  the  number  of  cover  plates. 

D.  Narrowing  of  flange  angles  and  necessitating  thereby  either  an  ad- 
ditional bracing  frame  or  an  increase  in  sectional  area  of  the  compression 
flange,  in  order  to  compensate  for  the  greater  ratio  of  unsupported  length 
to  width. 

E.  Possible  thickening  of  web  because  of  its  greater  depth. 

F.  Possible  encroachment  on  under-clearance  in  deck  spans,  or  raising 
of  grade  to  avoid  the  same. 

G.  Possible  difficulty  in  fabrication  or  shipment  in  case  of  long  or 
heavy  girders  because  of  excessive  depth. 

Any  of  these  changes  would  be  likely  so  to  upset  the  economics  of  the 
case  as  to  cause  a  material  decrease  in  the  theoretically  best  depth,  hence 
it  is  generally  advisable  to  adhere  to  the  rule  previously  given;  but  there 
are  occasionally  cases  where  a  saving  of  metal  may  be  effected  by  making 
the  web  depth  somewhat  smaller,  when  by  so  doing  a  web-splice  may  be 
avoided  or  lighter  stiffening  angles  may  be  adopted.  It  should  be  borne 
in  mind  that  there  is  quite  a  range  in  web-depths  over  which  the  theoretic 
minimum  weight  is  about  constant,  unless  the  thickness  of  the  shallower 
web  must  be  increased  on  account  of  shear;  hence  one  may  often  vary 
the  dimensions  of  a  plate-girder  materially  without  affecting  greatly 
the  matter  of  economics.  In  Chapter  XXI  of  "Bridge  Engineering" 
there  is  given  a  diagram  of  economic  depths  of  plate-girders  with  riveted 
end  connections. 

Concerning  economic  panel  lengths,  it  is  safe  to  make  the  following 
statement: — Within  the  limit  set  by  good  judgment  and  one's  inherent 
sense  of  fitness,  the  longer  the  panel  the  greater  the  economy  of  material 
in  the  superstructure.  Of  course,  when  one  goes  such  an  extent  as  to 
use  a  thirty-foot  panel  in  an  ordinary  single-track-railway  bridge  he 
exceeds  the  limits  referred  to,  because  the  lateral  diagonals  become  too 
long,  and  their  inclination  to  the  chords  becomes  too  flat  for  rigidity. 
Again,  an  extremely  long  panel  might  sometimes  cause  the  truss  diagonals 
to  have  an  unsightly  appearance  because  of  their  small  inclination  to 
the  horizontal, 

24 


There  is  another  mathematical  investigation  which  is  of  practical 
value.  It  relates  to  the  economic  lengths  of  spans,  and  was  first  demon- 
strated in  print  by  the  speaker  some  twenty-six  years  ago  in  "Indian  En- 
gineering, "  although  the  principle  was  announced  three  years  before  then 
in  the  first  edition  of  his  "General  Specifications  for  Highway  Bridges 
of  Iron  and  Steel".  Strange  to  say,  many  engineers  failed  to  see  that 
there  is  any  difference  between  this  principle  and  an  old  practice  of  over 
fifty  years'  standing.  The  principle  is  that  "for  any  crossing  the  great- 
est economy  will  be  attained  when  the  cost  per  lineal  foot  of  the  sub- 
structure is  equal  to  the  cost  per  lineal  foot  of  the  trusses  and  lateral 
systems".  The  old  practice  was  to  make  for  economy  the  cost  of  a  pier 
equal  to  the  cost  of  the  span  that  it  supports,  or,  more  properly,  equal 
to  one-half  of  the  cost  of  the  two  spans  that  it  helps  to  support.  Is  not 
the  difference  between  these  two  methods  perfectly  plain?  In  one  the 
cost  of  the  pier  is  made  equal  to  the  cost  of  the  trusses  and  laterals,  and 
in  the  other  it  is  made  equal  to  the  cost  of  the  trusses,  laterals,  and  floor 
system.  When  one  considers  that  the  cost  of  the  floor  system  is  some- 
times almost  as  great  as  one-half  of  the  total  cost  of  the  superstructure, 
he  will  recognize  how  faulty  the  old  method  was. 

As  just  indicated,  the  demonstration  referred  to  proves  that  in  any 
layout  of  spans,  with  the  conditions  assumed,  the  greatest  economy  will 
be  attained  when  the  cost  of  the  substructure  per  lineal  foot  of  bridge  is 
equal  to  the  cost  per  lineal  foot  of  the  trusses  and  lateral  systems.  Of 
course,  no  such  condition  as  a  bridge  of  indefinite  extent  ever  exists,  nor 
is  the  bed-rock  often  level  over  the  whole  crossing;  nevertheless  the  prin- 
ciple can  be  applied  to  each  pier  and  the  two  spans  that  it  helps  to  support 
by  making  the  cost  of  the  pier  equal  to  one-half  of  the  total  cost  of  the 
trusses  and  laterals  of  the  said  two  spans. 

The  principle  will  apply  also  to  trestles  and  elevated  roads;  for  in  the 
latter,  when  there  is  no  longitudinal  bracing,  if  we  make  the  cost  of  the 
stringers  or  longitudinal  girders  of  one  span  equal  to  the  cost  of  the  bent 
at  one  end  of  same,  including  its  pedestals,  we  shall  obtain  the  most 
economic  layout.  In  an  ordinary  railroad  trestle  consisting  of  alternating 
spans  and  towers,  it  will  be  necessary  for  greatest  economy  to  have  the 
cost  of  all  the  girders  in  two  spans  (one  span  being  over  the  tower)  plus 
the  cost  of  the  longitudinal  bracing  of  one  tower  equal  to  the  cost  of  the 
two  bents  of  said  tower,.. including  their  pedestals. 

The  economics  of  reinforced  concrete  bridges  have  not  received  much 
attention  from  technical  writers;  and  they  are  rather  difficult  to  deter- 
mine, as  the  quantities  involved  are  influenced  quite  largely  by  the  in- 
dividual taste  of  the  designer.  The  problem  is  also  complicated  by  the 
facts  that  the  unit  costs  of  the  various  portions  of  a  structure  may  be 
more  or  less  different,  and  that  the  unit  costs  of  different  types  of  con- 
struction may  be  decidedly  unlike.  In  general,  it  may  be  said  that  the 
unit  costs  are  lower  for  those  structures  which  have  the  simplest  form- 
work;  and  a  reduction  will  also  be  effected  by  decreasing  the  area  of  form- 
surface  per  cubic  yard  of  concrete.  For  instance,  in  the  case  of  a  wall 
or  slab  the  form-cost  per  cubic  yard  will  vary  practically  inversely  as  the 
thickness  of  the  said  wall  or  slab.  Evidently,  therefore,  it  is  desirable  to 

25 


concentrate  the  concrete  into  a  few  large  members,  rather  than  to  employ 
a  great  number  of  small  ones. 

It  should  be  noted  that  reinforcing  bars  less  than  %  in.  in  diameter 
command  higher  pound  prices  than  do  the  larger  bars.  The  extras  for 
these  small  bars  may  be  found  in  Engineering  News  the  first  of  each  month. 

Taking  up,  first,  girder  bridges  carried  on  columns,  the  following  points 
must  be  considered: 

First.     The  panel  length,  when  cross-girders  are  employed. 

Second.     The  number  and  spacing  of  the  longitudinal  girders. 

Third.     The  number  of  columns  per  bent. 

Fourth.     The  span  length. 

Fifth.     The  use  of  reinforced  concrete  piles  to  carry  the  footings. 

The  panel  length  adopted  is  usually  not  of  great  importance  from  the 
standpoint  of  economy.  Lengths  of  from  eight  to  ten  feet  are  generally 
employed;  but  a  considerable  variation  from  these  values  will  cause  little 
change  in  the  combined  cost  of  the  slabs  and  cross-girders.  A  reduction 
in  concrete  quantities  can  frequently  be  effected  by  using  long  panels, 
and  by  carrying  the  slabs  on  short  stringers  supported  by  the  floor-beams; 
but  the  extra  form-work  required  will  generally  overbalance  this  saving 
in  volume. 

The  number  and  spacing  of  the  longitudinal  girders  will  depend  upon 
the  width  and  the  height  of  the  structure,  the  span-length,  and  the  load 
to  be  carried.  For  a  high  structure  in  which  the  economic  span-length 
is  fairly  long,  it  will  nearly  always  be  found  best  to  employ  two  lines  of 
girders,  the  spacing  thereof  being  equal  to  about  five-eights  of  the  total 
width  of  the  structure;  but  for  bridges  much  over  sixty  (60)  feet  wide,  the 
use  of  three  or  even  four  lines  may  be  preferable.  The  slab  in  such  struc- 
tures is  carried  on  cross-girders  and  cantilever-beams.  For  a  low  bridge 
in  which  the  economic  span-length  is  short,  it  will  generally  be  the  cheapest 
to  omit  the  cross-girders,  except  at  the  bents,  and  to  employ  several  lines 
of  longitudinal  girders.  The  wider  the  structure,  the  more  likely  will 
this  arrangement  prove  to  be  economical;  and  very  heavy  loads  also  favor 
its  adoption.  For  a  structure  in  which  the  span-length  is  from  one-half 
to  two-thirds  of  the  width,  it  will  usually  make  little  difference  which  of 
the  two  types  is  adopted,  unless  the  height  is  rather  large;  and  even  in 
extreme  cases  the  variation  between  the  two  is  not  likely  to  exceed  ten 
per  cent.  Ordinarily,  it  will  be  found  more  desirable  to  use  two  lines 
of  girders,  with  cross-girders  and  cantilevers  about  eight  or  ten  feet 
centres. 

The  proper  number  of  columns  per  bent  depends  on  the  number  of 
longitudinal  girders.  When  there  are  only  two  lines,  two  columns  will, 
of  course,  be  employed.  When  there  arc  several  lines  of  girders,  there 
should  generally  be  one  column  per  girder  in  low  structures,  and  two 
columns  per  bent  in  higher  ones.  In  this  latter  case  a  heavy  cross-girder 
will  be  required  at  each  bent  to  carry  the  longitudinal  girders. 

The  economic  span-length  is  affected  by  the  height  and  the  load,  being 
larger  for  greater  heights  and  smaller  for  heavier  loads.  An  approximate 

26 


value  thereof  is  given  by  the  formula 


in  which  I  =  economic  span  length,  centre  to  centre  of  supports, 

w  =  load  per  lineal  foot  of  girder  (excluding  its  own  weight), 
and          h  =  fixed  height  of  structure. 

The  quantity  h  represents  in  any  given  case  the  height  which  is  fixed,  such 
as  the  height  from  grade  to  top  of  footing,  height  from  grade  to  bottom  of 
footing,  height  from  underside  of  girder  to  top  of  footing,  or  height  from 
underside  of  girder  to  bottom  of  footing,  as  the  case  may  be.  There  is 
always  a  considerable  range  of  lengths  for  which  the  quantities  remain 
nearly  constant.  The  formula  gives  values  a  trifle  greater  than  those  for 
which  the  quantities  are  a  minimum,  since  the  use  of  heavier  sections  will 
reduce  slightly  the  unit  costs  of  the  concrete. 

Reinforced-concrete  piles  should  be  used  under  footings  when  a  suit- 
able foundation  is  to  be  found  only  at  a  considerable  depth,  or  when  a  very 
large  footing  area  would  be  required  in  order  to  reduce  the  pressure  to 
a  proper  amount.  A  comparison  must  be  made  for  each  case  as  it  arises, 
allowing  properly  for  the  cost  of  the  column  shaft,  the  footing,  the  piles, 
and  the  excavation.  This  latter  item  must  not  be  overlooked. 

In  arches  the  problem  is  much  more  complicated  than  in  girder  spans. 
The  factors  that  affect  the  economic  lengths  are  the  cost  of  the  arch  ribs 
and  that  of  the  piers  and  abutments,  the  dividing  lines  between  them 
being  the  verticals  through  the  springing  points.  For  any  fixed  span- 
length  the  greater  the  rise,  up  to  a  limit  of  nearly  one-half  of  the  opening, 
the  smaller  will  be  the  costs  of  both  the  arch  and  the  piers  or  abutments 
which  sustain  it;  but  in  most  cases  the  distance  from  grade  to  ground  is 
too  small  to  permit  the  adoption  of  such  a  large  rise;  hence  the  problem 
generally  resolves  itself  into  a  determination  of  the  question,  "How  long 
can  the  span  be  made  economically  for  a  certain  limit  of  rise?"  This  will 
be  influenced  by  several  important  considerations,  among  which  may  be 
mentioned  the  following: 

A.  The  live  load  used. 

B.  The  amount  of  earth  fill,  if  any,  over  the  arches. 

C.  The  depth  of  the  foundations  for  the  piers  and  abutments  below 
the  springing  points. 

D.  The  cost  per  cubic  yard  for  putting  the  bases  of  piers  and  abut- 
ments down  to  a  satisfactory  foundation. 

E.  The  necessity  for  a  heavy  or  substantial  appearance  of  the  piers 
and  abutments. 

F.  The  height  to  which  the  large  pier  shafts  must  be  carried. 

G.  The  condition  of  the  arch  barrel  —  whether  solid  or  ribbed. 

H.  The  necessity,  or  otherwise,  of  adopting  certain  span-lengths  to 
meet  existing  conditions. 

Here  are  too  many  variables  for  a  theoretically  correct  economic  in- 
vestigation, hence  the  surest  and  most  satisfactory  way  to  proceed  is  to 
make  by  judgment  the  best  possible  layout  consistent  with  the  condi- 
tions, then  two  others,  one  involving  a  span-length  a  certain  number  of 

27 


feet  greater  and  the  other  a  span-length  the  same  number  of  feet  less, 
and  figure  the  costs  of  arches  and  piers  (or  abutments)  for  all  three  cases. 
Instead,  though,  of  increasing  and  decreasing  the  span  by  a  certain  num- 
ber of  feet,  it  may  be  necessary  to  reduce  and  augment  the  number  of 
spans  by  unity.  After  the  costs  of  the  arches  and  piers  or  abutments 
are  found  and  properly  combined,  the  cost  of  these  two  portions  of  the 
construction  per  lineal  foot  of  span  for  each  of  the  three  layouts  can  be 
computed  and  compared.  The  one  which  gives  a  minimum  will  indicate 
approximately  the  best  span-length  to  adopt. 

In  some  cases  it  will  prove  to  be  economic  to  make  the  middle  span 
of  the  bridge  a  certain  length  and  reduce  gradually  the  lengths  of  the 
spans  at  each  side.  If  the  configuration  of  the  crossing  will  permit  of 
a  symmetrical  layout  on  this  basis,  the  effect  will  prove  to  be  pleasing 
to  the  eye  and  generally  economic  of  first  cost,  especially  if  a  constant 
ratio  of  rise  to  span  be  maintained;  because,  as  far  as  cost  of  substruc- 
ture is  concerned,  the  overturning  moments  from  live  load  on  a  single 
span  only  and  from  inequality  of  dead  load  thrusts  are  kept  low,  owing 
to  the  fact  that  the  lighter  thrusts  in  the  smaller  span  act  with  a  greater 
lever  arm  than  do  the  heavier  thrusts  of  the  longer  span,  on  account  of 
higher  location  of  the  points  of  springing.  In  adopting  this  expedient, 
though,  care  has  to  be  exercised  to  prevent  the  principles  of  aesthetics  from 
being  violated. 

There  are  many  minor  economic  questions  that  arise  in  the  designing 
and  construction  of  bridges,  among  which  may  be  mentioned  the  economic 
greatest  lengths  of  different  types  of  spans;  the  character  of  approaches 
to  bridges;  column  spacing  in  bents  supporting  cross-girders  with  canti- 
lever brackets;  the  economic  functions  of  swing  spans,  cantilever  bridges, 
arches,  and  steel  trestles;  the  height  of  concrete  retaining  walls  at  which 
it  is  economic  to  begin  to  use  reinforcing;  the  relative  economics  in  em- 
ploying medium  steel,  soft  steel,  standard  steel,  and  alloy  steel  for  bridge 
superstructures;  the  effect  of  erection  on  the  economic  layout  of  spans;  the 
comparative  economics  of  rim-bearing  and  centre-bearing  swing-spans; 
economy  in  choice  of  metal  sections;  and  economy  in  shopwork.  These 
various  economic  questions  will  now  be  taken  up  in  the  order  enumerated. 

Comparing  rolled  I-beam  and  plate-girder  deck  spans  for  modern 
heavy  live  loads,  the  weights  of  metal  are  about  equal  for  spans  of  fifteen 
feet;  but  the  former  are  cheaper  per  pound  than  the  latter  by  about 
four-tenths  (0.4)  of  a  cent,  consequently  the  costs  per  lineal  foot  erected 
are  equal  for  a  span  of  about  twenty  feet. 

Comparing  deck  plate-girders  and  through,  riveted  truss-spans,  for 
which  there  is  usually  a  difference  of  about  one-half  cent  per  pound  erected 
in  favor  of  the  former  the  weights  of  metal  per  lineal  foot  are  the  same 
for  spans  of  one  hundred  and  fifteen  (115)  feet,  which  is  about  the  ex- 
treme limit  of  length  for  plate-girder  spans  shipped  in  one  piece;  hence 
it  may  be  concluded  that  for  all  practicable  lengths,  deck  plate-girder  spans 
are  more  economic  than  through,  riveted  truss-spans.  Besides,  the  use 
of  such  deck  spans  effects  a  great  economy  in  the  substructure  by  reduc- 
ing the  length  of  each  pier  from  six  to  ten  feet,  the  longer  the  span,  of 

28 


course,  the  less  the  reduction.  It  generally  reduces  also  the  heights  of 
the  piers. 

Comparing  half-through,  plate-girder  spans  and  through,  riveted  truss- 
spans,  for  which  there  is  a  difference  of  about  two-tenths  (0.2)  of  a  cent 
per  pound  erected  in  favor  of  the  former,  the  weights  of  metal  per  lineal 
foot  are  the  same  for  spans  of  seventy  (70)  feet,  but  the  costs  per  foot 
are  about  equal  for  spans  of  seventy-five  (75)  feet.  However,  as  plate- 
girder  spans  are  in  many  respects  more  satisfactory  than  short,  through, 
riveted  spans,  the  dividing  point  is  generally  placed  at  about  one  hundred 
(100)  feet. 

Comparing  Pratt  and  Petit  truss-spans,  for  which  there  is  no  difference 
worth  mentioning  in  the  pound  prices  of  the  metal,  the  weights  per  foot 
(and  therefore  the  costs)  are  alike  for  single-track  spans  of  three  hundred 
(300)  feet,  and  for  double-track  spans  of  three  hundred  and  fifty  (350) 
feet;  but  both  constructive  and  aesthetic  reasons  necessitate  limiting  the 
lengths  of  Pratt  trusses  to  about  three  hundred  and  twenty-five  (325)  feet. 

The  economics  of  approaches  to  bridges  will  involve  the  question  of 
whether  it  is  best  and  cheapest  to  build  earth  embankments,  timber 
trestles,  or  steel  viaducts,  and  at  what  heights  it  would  pay  to  change 
from  one  kind  to  the  other.  It  can  be  readily  solved  by  employing  the 
numerous  diagrams  of  Chapters  LIII  to  LVI,  inclusive,  of  "Bridge  En- 
gineering". 

The  economics  of  column  spacing  for  bents  when  cantilever  brackets 
are  employed  is  an  interesting  little  problem,  but  the  final  determination 
must  be  in  accordance  with  good  judgment  as  well  as  economy;  for  if 
the  spacing  be  too  small,  rigidity  is  likely  to  be  sacrificed.  Upon  certain 
assumptions  of  approximate  correctness,  the  mathematical  solution  of 
this  problem  is  a  possibility;  but  the  equations  involved  would  be  so 
complicated  that  it  is  much  better  for  any  particular  case  to  assume  two 
or  three  spacings,  compute  the  total  weight  of  metal  in  the  bent  for  each, 
and  find  the  one  which  will  give  approximately  the  least  weight  of  metal. 
If  the  columns  are  placed  at  the  quarter  points  of  the  beam,  the  dead  load 
bending  moment  at  the  middle  will  be  approximately  zero;  and  if  the 
effect  of  stress  reversion  is  ignored,  the  direct  and  reverse  bending  moments 
for  the  central  portion  of  the  beam  will  be  equal,  and  this  arrangement 
would  be  about  the  most  economical  possible.  But  if  the  reversion  is 
considered,  the  sectional  area  of  the  middle  portion  of  the  beam  must  be 
greater  than  that  of  the  outside  portions,  hence  for  economy  its  length 
should  be  somewhat  less  than  one-half  of  the  total,  and  the  columns 
would  then  be  spaced  somewhat  closer  than  when  they  are  located  at  the 
quarter  points.  The  fact  that  the  brackets  are  usually  lighter  near  the 
outer  ends  than  at  the  inner  ones  would,  for  economy,  tend  to  draw  the 
columns  together;  but  on  the  other  hand  this  would  increase  the  weight 
of  the  splices  and  connecting  details.  The  proper  column  spacing  to  adopt 
will  depend  upon  the  length  of  the  columns;  for  it  is  easily  conceivable 
that  the  structure  could  be  so  high  and  so  narrow  that  the  quarter-point 
spacing  would  be  too  close  for  proper  resistance  to  wind  pressure.  Again, 
in  such  a  case  the  wind  load  might  be  so  great  as  to  necessitate  an  increase 
in  column  section  above  that  required  to  care  for  the  live  and  dead  load 

29 


stresses  only;  and  thus  the  effect  of  wind  pressure  would  enter  the  eco- 
nomic study.  It  will  be  found  in  most  cases  that  it  is  inadvisable  to  space 
the  columns  much  less  than  one-half  of  the  total  length  of  the  beam. 

The  economic  functions  of  swing  spans  are  somewhat  difficult  to  for- 
mulate. The  minimum  perpendicular  distance  between  central  planes  of 
trusses  for  first-class  construction  should  be  the  same  as  for  simple-truss 
spans, — viz.,  one-twentieth  of  the  span  length.  It  is  evident,  of  course, 
that  the  narrower  the  bridge  the  less  it  will  weigh  and  cost.  The  truss 
depths  at  ends  of  through  swing  bridges  are  generally  determined  by  the 
clearance  requirements;  but  in  long  spans  it  is  sometimes  advisable,  for 
the  sake  of  vertical  stiffness  and  to  avoid  the  raising  of  span-end  from  a 
load  on  the  other  arm,  to  make  the  said  depths  still  greater.  As  a  rule, 
this  increase  is  not  of  an  uneconomic  nature.  For  long  spans,  or  those 
exceeding,  say,  four  hundred  (400)  feet,  the  truss  depth  at  outer  hips 
should  be  about  one-fourteenth  (3^)  or  one-fifteenth  (^)  of  the  total 
span  length.  The  truss  depth  at  the  inner  hips  should  generally  be  from 
one-ninth  (J)  to  one-tenth  (^)  of  the  total  span  length;  and  when 
towers  are  used,  their  height  should  generally  be  from  one-sixth  (£)  to 
one-seventh  (^)  of  the  span.  Of  course,  the  aesthetic  features  of  the 
design  should  govern  greatly  the  determination  of  all  these  depths;  and, 
fortunately,  any  moderate  change  in  them  does  not  affect  materially 
their  economics. 

In  swing  spans  it  is  evident  that,  as  far  as  is  consistent  with  safety,  the 
diameter  of  the  drum  for  economy  should  be  made  as  small  as  possible, 
not  only  because  this  effects  a  saving  of  metal,  but  also  because  it  reduces 
the  diameter,  and  therefore  the  cost,  of  the  pivot  pier.  For  spans  of  mod- 
erate length  and  width  there  is  generally  a  small  economy  in  centre- 
bearing  swing-spans  over  rim-bearing  ones,  especially  as  the  former  some- 
times permit  of  smaller  pivot  piers,  but  the  difference  is  often  inconsid- 
erable. There  is  a  limit  to  the  size  of  centre-bearing  swing-spans  due  to 
the  objectionable  feature  of  concentrating  great  loads  upon  small  areas 
and  to  the  necessity  in  the  case  of  very  wide  spans  for  excessively  heavy 
cross-girders.  The  question  of  economics  between  the  two  styles  of  swings 
is  one  that  has  to  be  determined  for  each  special  case  as  it  arises  by  pre- 
paring actual  estimates  and  not  by  a  priori  reasoning. 

In  respect  to  the  economics  of  cantilever  bridges  the  following  may  be 
stated: 

FIRST.  The  economic  length  of  the  suspended  span  is  about  three- 
eights  (f )  of  the  length  of  the  main  opening,  but  a  considerable  increase 
or  decrease  of  this  proportion  does  not  greatly  change  the  total  weight 
of  the  metal. 

SECOND.  The  most  economic  length  of  anchor  arms,  where  the  total 
length  between  centres  of  anchorages  is  given,  and  when  the  main  piers 
can  be  placed  wherever  desired,  is  one-fifth  (£)  of  the  said  total  length. 
By  keeping  the  anchor  arms  short,  the  top  chords  may  be  built  of  eye-bars, 
provided  that,  with  the  usual  allowance  for  impact,  there  is  no  reversion 
of  chord  stress;  and  this  effects  quite  an  economy  of  metal.  But  it  is 
conceivable  that  cases  might  arise  where,  from  danger  of  washout  of 

30 


falsework,  eye-bar  top  chords  would  be  objectionable;  hence  this  method 
of  economizing  must  be  used  with  caution. 

THIRD.  In  respect  to  the  economic  length  of  anchor-span  in  a  succession 
of  cantilever  spans,  it  may  be  stated  that  within  reasonable  limits  the 
shorter  such  anchor-spans  are  the  greater  will  be  the  economy  involved; 
but,  generally,  navigation  interests  will  prevent  their  being  built  as  short 
as  might  be  desired.  If  permissible,  they  may  be  made  so  short  that, 
as  in  the  case  of  anchor-arms,  eye-bars  may  be  used  for  the  top  chords, 
thus  effecting  a  decided  economy  of  metal,  although  shortening  the  anchor- 
span  increases  proportionately  the  stresses  on  the  web  members  and  the 
weights  thereof. 

The  question  of  what  is  the  economic  limit  of  length  of  simple-truss 
spans  as  compared  with  cantilevers  is  still  a  mooted  one.  Professors 
Merriman  and  Jacoby  place  it  in  the  neighborhood  of  six  hundred  (600) 
feet,  but  the  speaker  has  had  occasion  to  compare  simple-truss  spans  of 
seven  hundred  (700)  and  eight  hundred  (800)  feet  with  the  corresponding 
cantilever  structures,  and  has  found  the  former  more  economic.  The 
continuity  of  cantilever  spans  in  resisting  wind  loads  lowers  the  require- 
ment for  minimum  width  from  one-twentieth  (^)  to  about  one  twenty- 
fifth  (^)  of  the  greatest  span-length,  and  hence,  because  of  substruc- 
ture considerations,  gives  an  advantage  to  the  cantilever  type  that  in 
certain  extreme  cases  will  more  than  offset  its  disadvantages  of  greater 
weight  of  truss  metal. 

There  are  certain  legitimate  economies  that  may  be  employed  in  the 
designing  of  cantilever  bridges,  among  which  may  be  mentioned  the 
following: 

A.  The  wind  pressure  assumed  in  computing  the  erection  stresses 
may  be  taken  lower  than  that  given  in  the  specifications  for  the  finished 
structure,  provided  that  the  full  wind  pressure  would  not  overstress  any 
of  the  metal  seriously  or  involve  any  risk  of  disaster  during  erection. 
A  stress  of  three-quarters  of  the  elastic  limit  of  the  metal  applied  a  few 
times  during  erection  would  do  no  harm,  and  the  chance  of  there  being 
in  that  limited  time  any  wind  pressure  at  all  approaching  in  magnitude 
that  specified  is  very  small.    This  lowering  of  the  intensity  of  wind  pres- 
sure may  be  the  means  of  avoiding,  in  a  perfectly  legitimate  manner, 
the  increasing  of  the  sections  of  a  number  of  truss  members  because  of 
erection  stresses;  but  such  economizing  should  be  done  with  caution  after 
a  thorough  consideration  of  its  greatest  possible  effects. 

B.  A   certain  amount  of  metal  can  sometimes  be  saved  by  splaying 
the  trusses  between  the  main  piers  and  the  ends  of  the  cantilever  and 
anchor  arms;  but  unless  the  amount  thereof  be  fairly  large,  the  extra 
pound  price  of  the  metalwork  in  the  cantilever-  and  anchor-arms  due  to 
the  said  splaying  may  more  than  offset  the  value  of  the  reduction. 

C.  A  small  economy  may  sometimes  be  accomplished  by  omitting 
during  erection  from  the  cantilever  portion  of  the  structure  all  parts  that 
are  not  essential  to  its  strength  before  the  coupling  of  the  cantilever  ends 
is  effected,  thus  reducing  the  erection  stresses  a  little. 

D.  Solitary  piers  or  large  pedestals  under  the  main  vertical  posts 
are  sometimes  just  as  satisfactory  in  every  way  as  long,  continuous  piers, 

31 


especially  if  a  connecting  wall  of  reinforced  concrete  between  them  be 
employed.  Generally  they  will  be  found  to  involve  a  large  saving  in  the 
cost  of  the  substructure. 

E.  In  very  wide  cantilever  bridges  it  might  sometimes  be  advisable  to 
adopt  intermediate  trusses  so  as  to  economize  materially  in  the  weight  of 
the  floor-beams  and  a  trifle  in  that  of  the  trusses,  also  because  of  the  con- 
sequent reduction  in  dead  load,  but  mainly  so  as  to  keep  within  reasonable 
limits  the  sizes  and  weights  of  the  pieces  to  be  handled  and  thus  economize 
on  the  size  of  the  traveler  and  the  cost  of  the  erecting  machinery.    On  the 
other  hand,  though,  increasing  the  number  of  trusses  is  likely  to  increase 
a  little  the  percentage  of  weight  of  truss  details;  but  where  the  sections 
of  members  are  large  this  increase  would  be  small.     In  case  the  wind 
stresses  are  an  important  factor  in  the  proportioning  of  the  truss  members, 
the  employment  of  an  interior  truss  or  interior  trusses  might,  by  the 
reduction  in  areas  of  chord  sections,  cause  such  relatively   large    wind 
stresses  on  the  chords  of  the  exterior  trusses  that  the  additional  metal 
required  to  take  care  of  them  would  offset  all  the  saving  obtained  in  the 
ways  just  mentioned. 

F.  In  long-span  cantilever  bridges  the  stresses  on  the  truss  members 
that  rest  upon  the  piers  should  be  divided  among  as  many  such  members 
as  possible  by  using  an  inclined  strut  on  each  side  as  well  as  a  vertical 
post  instead  of  carrying  all  the  loads  to  the  top  of  the  latter  by  tension 
members,  as  was  done  in  the  design  of  the  ill-fated  Quebec  bridge.    Again, 
if  a  lowering  of  the  inner  ends  of  the  cantilever  arms  be  permissible,  the 
inclining  of  the  end  sections  of  the  bottom  chords  to  the  horizontal  will 
take  up  a  portion  of  the  load  that  is  carried  to  the  pier  and  thus  will 
reduce  the  stresses  on  the  vertical  and  inclined  posts  assembling  there. 
This  last  feature  reduces  also  the  total  cost  of  the  masonry  by  diminishing 
the  height  of  the  main  piers,  and  saves  placing  the  tops  of  the  trusses 
at  an  abnormal  height  above  the  water. 

G.  If  there  be  any  choice  between  the  riveted  and  the  pin-connected 
types  of  construction  for  any  cantilever  bridge,  it  is  generally  better  to 
adopt  the  latter,  because,  as  cantilever  bridges  are  usually  employed  for 
long  spans  only,  pin-connected  work  is  the  more  suitable.    Again,  it  is  a 
little  lighter  than  riveted  work,  and  therefore  the  dead  load  on  the  structure 
would  be  somewhat  less.     On  the  other  hand,  the  riveted  construction 
is  so  much  more  rigid  than  the  pin-connected  that  it  is  preferable  to 
adopt  it  whenever  the  conditions  permit;  besides,  in  the  riveted  work  it 
is  not  necessary  to  stiffen  any  truss  members  for  erection,  although  it 
might  be  obligatory  to  increase  a  few  of  their  sectional  areas. 

H.  Very  large  compression  members  should  be  made  of  box  section 
so  as  to  do  away  with  latticing.  This  not  only  effects  an  improvement 
in  the  design,  but  also  saves  some  metal,  although  the  details  required  at 
the  panel  points  to  distribute  the  stresses  from  the  cut  cover  plates  tend 
to  offset  the  saving  in  weight  of  lattice  bars  and  stay  plates. 

Questions  of  erection  often  not  only  affect  the  economic  layouts  of 
crossings  but  also  determine  the  character  of  the  spans  to  be  adopted. 
For  instance,  if  the  danger  from  washout  of  falsework  be  great,  either  a 
cantilever  or  a  semi-cantilever  structure  may  be  better  than  one  of  simple 

32 


spans,  or  a  pin-connected  structure  may  be  preferable  to  a  riveted  one, 
even  if  the  computations  of  cost  made  upon  the  basis  of  good  luck  in 
erection  indicate  that  the  contrary  is  the  case.  Again,  the  chance  of  not 
getting  the  substructure  finished  before  high  water  or  bad  weather  causes 
a  cessation  or  partial  cessation  of  work  might  so  affect  the  layout  of  spans 
for  a  bridge  as  to  increase  materially  the  cost  thereof;  therefore,  the 
expense  involved  by  taking  precautions  to  avoid  possible  delay  would  be 
in  the  nature  of  true  economy. 

In  the  proportioning  of  main  members  of  bridges,  and  even  occasionally 
in  the  detailing,  small  economies  may  be  effected  by  choosing  the  regular 
and  least  expensive  sections.  Plates  and  angles  are  at  times  cheaper  than 
channels  or  I-beams,  and  at  other  times  more  expensive.  Z-bars  are 
sometimes  higher  and  are  always  difficult  to  obtain.  Deck  beams  are  in- 
variably high  priced,  and  tees  are  generally  so.  Many  designers  are  not 
aware  that  I-beams  over  fifteen  (15)  inches  deep  cost  one-tenth  (^0)  of 
a  cent  per  pound  more  than  those  fifteen  (15)  inches  and  under  in  depth, 
and  that  angles  having  one  or  both  legs  longer  than  6  inches  are  subject 
to  the  same  increase.  There  is  a  long  list  of  special  prices,  too,  on  very 
small  angles.  Not  infrequently  it  will  be  cheaper  to  use  the  larger  of  two 
small  angles,  even  though  more  weight  be  involved;  and  special  angles 
such  as  those  of  7  by  3^  in.  section  are  always  more  expensive  than  the 
standards,  besides  being  more  difficult  to  obtain.  Current  prices  of  the 
various  sections  are  to  be  found  in  Engineering  News  the  first  of  each 
month.  Since  the  organization  of  the  United  States  Steel  Corporation, 
the  variations  in  pound  prices  of  the  numerous  shapes  of  bridge  metal  in 
this  country  are  less  than  they  used  to  be;  but  they  are  still  sufficient  to 
make  a  material  difference  in  the  cost  of  structure:  whereas,  for  Canadian 
and  other  foreign  work,  very  large  differences  may  be  created  by  the 
selection  of  the  material,  owing  to  the  variation  in  the  customs  duties. 
It  behooves  the  expert  bridge  designer  to  keep  posted  concerning  varia- 
tions in  metal  prices  and  import  duties  for  the  different  sections.  The 
Bethlehem  Steel  Company  manufactures,  by  means  of  a  combination  of 
vertical  and  horizontal  rolls  acting  simultaneously,  some  special  sections 
for  I-beams  that  are  exceedingly  light  for  their  strength;  and,  although 
the  company  asks  a  small  extra  price  for  such  sections,  it  generally  proves 
economical  to  employ  them. 

The  duplication  of  a  whole  structure,  or  any  parts  thereof,  effects  a 
large  proportionate  saving  in  the  shop.  Of  course,  if  two  spans  or  other 
units  can  be  made  alike,  entire  groups  of  drawings  are  saved;  and  it  is  a 
large  part  of  the  function  of  the  detail  shop  draftsman  to  duplicate  in- 
dividual parts  and  to  group  partially-unlike  members.  By  duplication, 
in  addition  to  a  saving  in  drawings,  there  is  a  saving  of  templets,  a  saving 
of  shop  supervision,  a  saving  of  the  writing  of  shop  bills,  a  saving  of  making 
extra  material  lists,  a  large  saving  in  errors,  and  a  considerable  saving  in 
the  field  due  to  the  avoidance  of  loss  of  time  in  the  selection  of  the  proper 
parts;  for  if  there  is  much  duplication,  there  is  much  more  possibility  of 
the  right  parts  being  at  hand.  Duplication  extends  into  very  small  details; 
in  beam  work  the  end  connections  are  made  alike,  and  instead  of  being 
shown  on  the  drawings,  their  numbers  only  are  given.  Likewise  the  tem- 

33 


plets  for  such  end  connections  are  made  permanent;  and  they,  too,  are 
referred  to  only  by  number  and  are  used  over  and  over  again.  On  large 
structures,  batten  plates,  lattice  bars,  and  other  similar  and  oft-repeated 
elements  can  be  duplicated  with  great  advantage.  For  instance,  identical 
lattice-bars  save  the  resetting  of  the  gauge  on  the  lattice-bar  punch,  and 
also  the  labor  of  selecting  in  assembling  the  material,  besides  considerable 
expense  in  handling.  It  may  at  times  require  more  material  to  duplicate 
the  parts  of  a  structure,  and  yet  it  may  result  in  a  net  saving  in  the 
cost  of  construction;  for,  although  the  metal  be  ordered  by  the  pound,  if 
the  evidence  of  duplication  of  shopwork  is  made  clear  in  the  drawings  sub- 
mitted to  bidders,  a  lower  pound  price  will  be  named. 

Blacksmith  work  of  any  kind  is  always  the  most  expensive  work  in  a 
bridge  shop,  and  it  should  be  avoided  to  the  utmost,  not  only  because  it  is 
not  commonly  well  done  but  also  because  it  costs  heavily  in  the  drawing 
room,  in  the  templet  room,  in  the  forge  shop,  and  in  punching,  fitting, 
and  assembling.  If  forging  is  essential,  it  should  be  done  in  duplicate  as 
much  as  possible,  so  that  dies  may  be  made. 

There  is  a  small  economy  or  the  reverse  involved  in  the  crimping  of 
stiffening  angles  for  plate-girders;  and  the  officers  of  the  different  bridge 
shops  have  widely  varying  ideas  as  to  whether  it  is  better  or  not  to  crimp 
them.  The  economy  will  depend  upon  their  strength  and  the  amount  of 
offset,  for  the  question  involved  is  whether  the  cost  of  crimping  the  ends 
does  or  does  not  exceed  that  of  furnishing  and  putting  in  the  filling  plates. 
The  cost  of  the  freight  on  the  filling  plates  is  often  the  determining  factor 
in  settling  whether  it  is  finally  more  economic  or  otherwise  to  crimp  stiff- 
ening angles,  and  this  feature  of  the  question  should  be  borne  in  mind  by 
the  designer.  This  matter  of  cost  of  freight  and  other  transportation  of 
metal  to  bridge  site  applies  to  the  design  of  a  bridge  as  a  whole  as  well 
as  to  the  question  of  crimping. 

There  is  often  a  material  difference  between  the  lightest  possible  bridge 
and  the  most  economic  one,  not  only  on  account  of  the  reduction  of  cost 
of  fabrication  but  also  because  of  that  of  erection;  and  the  designer, in 
order  to  obtain  the  best  possible  results  for  all  cases,  must  be  well  posted 
on  all  the  important  details  of  both  shopwork  and  field  work.  He  should 
know  almost  instinctively  what  is  easy  and  what  is  difficult  to  manufac- 
ture and  to  erect;  and  especially  should  he  recognize  when  rivets  can  and 
when  they  cannot  be  driven  by  the  various  kinds  of  apparatus  used  in 
shop  and  field. 

In  the  design  of  new  bridges  to  replace  old  ones,  the  erection  should  be 
given  full  and  thorough  consideration,  since  a  large  amount  of  the  labor 
of  replacing  the  old  structure  under  traffic  may  be  saved  if  the  new  one 
have  panels  of  such  length  as  not  to  interfere  with  the  metalwork  of  the 
old  bridge.  There  are  many  other  ways  in  which  advantage  may  be  gained 
by  thoroughly  considering  the  erection  at  the  time  the  new  structure  is 
designed,  such,  for  instance,  as  the  supporting  of  the  old  stringers  on  ad- 
vantageously located  falsework  until  the  new  girders  can  be  placed,  and 
the  shipping  of  the  plate-girder  spans  riveted  up  complete  instead  of  re- 
quiring that  they  be  assembled  in  the  field. 

In  all  work  of  designing,  the  cost  of  the  materials  at  the  site  should  be 

34 


studied  very  carefully,  since  local  prices  will  often  enable  the  designer  to 
effect  a  great  saving.  Where  the  work  is  scattered  over  a  wide  field,  the 
matter  of  cost  of  materials  becomes  exceedingly  important  and  often 
changes  the  type  of  the  structure.  For  instance,  in  designing  a  highway 
bridge  for  the  Western  Coast,  it  should  be  remembered  that  steel  stringers 
become  very  costly  as  compared  with  the  lower-priced  wooden  stringers 
of  that  country.  The  opposite  conditions  obtain  in  the  eastern  part  of 
the  United  States.  The  prices  of  gravel  for  concrete  work,  or  of  very 
cheap  stone,  may  affect  the  type  of  piers  employed.  The  engineer  should 
know  markets  even  better  than  the  contractor,  but  commonly  he  does 
not,  and  he  will  often  demand  an  expensive  material  where  a  cheaper  one 
would  serve  his  purpose  quite  as  well.  Rough  averages  of  prices  per  unit 
in  place  are  very  apt  to  produce  flaws  in  the  economy  of  a  design. 

There  is  an  economic  feature  of  bridge  building  that  is  worthy  of  special 
mention,  in  that  it  effects  a  large  saving  in  first  cost,  maintenance,  and 
repairs,  often  for  a  number  of  years.  It  is  the  designing  of  cantilever 
brackets  to  carry  in  the  future  wagonways,  footwalks,  and  even  street 
railways,  and  omitting  putting  them  in  until  required,  but  providing  all 
the  rivet-holes  for  the  future  connections.  In  such  cases,  of  course,  the 
trusses  must  be  made  strong  enough  to  carry  the  additional  live  and  dead 
loads,  and  the  counterbracing  must  be  figured  for  both  the  future  and  the 
immediate  dead  loads. 

A  question  sometimes  arises  as  to  whether  it  is  more  economic  to  sup- 
port a  pavement  on  buckled  plate  or  on  reinforced  concrete.  The  latter 
is  cheaper  for  trestles  and  short  spans,  but  not  for  long  ones.  However, 
the  deterioration  of  the  buckled  plates,  due  to  moisture  and  smoke  fumes, 
should  receive  adequate  consideration.  Moreover,  the  latest  experience 
shows  that  very  heavy  concentrated  live  loads  are  liable  to  spring  the 
buckled  plates  and  break  up  the  paving. 

Some  of  the  most  modern  problems  in  bridge  economics  are  those  due 
to  the  advent  of  reinforced  concrete  construction.  For  instance,  in  high- 
way bridge  building  there  arises  the  general  question  as  to  whether  it  is 
advisable  to  adopt  reinforced  concrete  or  steel;  and  for  spans  under  one 
hundred  feet  in  length,  when  due  consideration  is  paid  to  the  factors 
of  maintenance,  depreciation,  and  repairs,  the  former  will  usually  be 
found  the  more  economic.  In  the  future  this  limit  of  span-length  for 
economy  will  certainly  continue  to  increase;  and  probably  even  today 
it  has  been  passed  in  some  localities. 

Another  problem  is  whether  in  reinforced  concrete  construction  it  is 
preferable  to  adopt  the  arch  or  the  girder  type.  Unless  the  spans  are 
quite  long,  the  latter  will  generally  be  the  cheaper,  but  the  former  is  the 
more  aesthetic,  although  by  curving  the  bottoms  of  the  concrete  girders, 
as  was  done  on  the  Twelfth  Street  Trafficway  Viaduct  in  Kansas  City,  a 
very  pleasing  effect  can  be  secured. 

Another  economic  problem  is  whether  to  adopt  a  wooden  or  a  reinforced 
concrete  floor  in  a  steel  highway  bridge;  and,  when  danger  from  fire,  cost 
of  maintenance,  etc.,  are  considered,  the  decision  should  invariably  be  in 
favor  of  the  permanent  construction. 

Since  the  late  occurrence  of  partial  destruction  by  fire  of  several  large 

35 


highway  bridges  carrying  creosoted  block  pavement  resting  on  creosoted 
planks,  the  question  has  arisen  as  to  how  much  more  it  would  have  cost 
to  rest  the  pavement  on  reinforced  concrete.  The  layman  has  an  idea 
that  the  amount  is  very  small,  being  merely  the  difference  between  the 
value  of  the  reinforced  concrete  slab  and  that  of  the  creosoted  planks; 
but  such  is  far  from  being  the  case,  for  the  large  difference  between  the 
weights  of  the  two  bases  adds  materially  to  the  dead  load  that  has  to  be 
carried  by  both  the  floor  system  and  the  main  girders  or  trusses. 

In  the  case  of  a  steel  viaduct,  the  question  sometimes  comes  up  as  to 
the  economics  of  making  the  bents  of  reinforced  concrete  instead  of  steel ; 
and  for  heights  not  greater  than  forty  or  fifty  feet  the  concrete  is  likely 
to  win;  but  with  braced  towers  the  steel  will  generally  prove  the  cheaper. 
In  solitary  bents  of  reinforced  concrete  attention  must  be  paid  to  the 
bending  effect  of  longitudinal  thrust,  and  this  is  likely  to  prove  an  im- 
portant factor  in  the  determination  of  the  economics  of  the  layout. 

There  is  an  economic  question  to  which,  as  yet,  but  little  attention  has 
been  paid, — viz.,  the  comparative  costs  of  cantilever  andsuspension  bridges. 
Until  1911  nothing  of  any  value  had  been  published  concerning  the  length 
of  span  at  which  a  suspension  bridge  becomes  cheaper  than  a  cantilever, 
each  bridge  specialist  having  had  a  vague  idea  of  his  own  concerning  the 
question.  The  speaker  for  years  has  believed  the  dividing  length  to  be  in 
the  neighborhood  of  2,000  feet,  but  has  recognized  that  it  will  vary  con- 
siderably for  different  crossings  on  account  of  the  governing  conditions. 
If  the  question  were  one  of  superstructure  alone,  it  would  readily  be  capable 
of  solution,  but  the  substructure  plays  an  exceedingly  important  part 
therein.  Dr.  Steinman  places  the  dividing  span-length  (based  solely  on 
economic  reasons)  between  cantilever  and  suspension  bridges  at  about 
seventeen  hundred  (1,700)  feet;  but  certain  assumptions  differing  from 
his  concerning  schedule  prices  and  other  ruling  conditions  would  have 
increased  somewhat  this  limit. 

The  economic  depth  for  stiffening  trusses  of  suspension  bridges  has 
been  determined  theoretically  by  Dr.  Steinman.  He  finds  that  it  is  about 
one-fortieth  (^)  of  the  span,  and  states  that  this  is  somewhat  higher 
than  the  average  of  past  practice,  probably  because  most  designs  have  been 
a  compromise  between  the  demands  of  economy  and  those  of  aesthetics. 
In  his  opinion,  the  Williamsburg  Bridge,  which  is  the  only  long-span 
structure  conforming  to  this  economic  ratio,  is  marred  in  appearance  by 
the  excessive  depth  of  the  stiffening  trusses.  This  limit  does  not  strike 
one  as  being  very  high,  though,  considering  the  fact  that  the  trusses  are 
generally  through  ones  and  that  they  must  provide  a  clear  headway 
ranging  between  twenty  and  twenty-five  feet.  If  twelve  hundred  feet 
be  taken  as  the  minimum  span-length  for  which  it  would  be  legitimate  to 
consider  the  adoption  of  a  suspension  bridge  for  railway  traffic,  the  eco- 
nomic truss  depth  would  be  thirty  feet,  which  is  a  little  shallower  than 
it  is  practicable  to  adopt  for  a  double-track  bridge  with  floor-beams  and 
portal  bracing  that  have  ample  depths  for  rigidity.  A  serious  objection 
to  employing  shallow  deck  stiffening  trusses  is  their  unsightly  appearance. 
All  things  considered,  it  is  generally  advisable  to  make  the  truss  depth 

36 


as  shallow  as  the  governing  conditions  will  allow,  provided  that  the  eco- 
nomic depth  be  not  varied  from  too  radically. 

The  inferior  limiting  ratio  of  distance  between  central  planes  of  stiff- 
ening trusses  to  span-length  has  not  yet  received  due  attention  by  engi- 
neering writers.  The  speaker  is  of  the  opinion  that  it  ought  to  be  about 
as  one  is  to  thirty,  that  for  simple  spans  being  as  one  is  to  twenty.  There 
are  two  good  reasons  for  placing  a  minimum  limit  to  this  ratio, — viz.,  to 
avoid  vibration  and  to  make  the  various  compression  chords,  which,  in 
a  way,  form  one  long  strut  of  the  same  length  as  the  span,  have  a  reason- 
able ratio  of  length  to  radius  of  gyration.  For  the  thirty-to-one  limit  the 
ratio  of  length  to  radius  of  gyration  would  be  about  sixty,  which  is  well 
within  the  bounds  of  good  practice  in  strut  proportioning. 

The  economic  cable-rise  for  many  years  has  been  recognized  as  vary- 
ing from  one-tenth  to  one-eighth  of  the  span  length.  For  bridges  in  which 
the  side  spans  are  without  suspenders,  Dr.  Steinman  finds  that  it  is  about 
one-ninth  of  the  main  span,  and  for  those  in  which  the  side  spans  are 
suspended  from  the  backstays  it  is  about  one-eighth  thereof. 

The  number  of  arch  bridges  built  up  to  the  present  time  is  compara- 
tively so  small,  and  the  economic  studies  thus  far  made  on  arches  have 
been  of  such  an  approximate  character,  that  but  little  reliable  information 
concerning  the  comparative  economics  of  the  various  types  is  available. 
There  is  a  general  impression  that  the  smaller  the  number  of  hinges  the 
greater  the  economy,  but  there  are  conflicting  opinions  concerning  that 
view.  Again,  it  is  probable,  but  not  yet  proved,  that  for  exactly  similar 
conditions  of  layout  and  loading  a  cantilever-arch  bridge  is  a  little  less 
expensive  than  an  ordinary  arch  with  two  flanking  simple  spans.  Finally, 
the  three  standard  kinds  of  ribs  for  fairly  long  spans  in  the  order  of  their 
economy  are  generally  supposed  to  be  the  spandrel-braced,  the  braced- 
rib,  and  the  solid-rib  types;  but  differences  in  the  existing  conditions  at 
crossings  may  vary  this  order  in  certain  cases. 

Another  economic  question  in  bridge  engineering  that  has  arisen  of 
late  years  is  the  economics  of  movable  spans,  or  the  choice  for  any  crossing 
between  the  swing,  bascule,  and  vertical-lift  types.  The  settlement  of 
this  question  is  by  no  means  an  easy  matter,  for  it  will  depend  greatly 
upon  the  special  conditions  affecting  the  particular  crossing  under  con- 
sideration. When  the  swing-span  type  is  pitted  against  either  of  the 
others,  the  first  point  to  determine  is  what  proportionate  length  of  single 
opening  is  equivalent  to  the  two  openings  afforded  by  the  rotating  draw. 
This  is  a  matter  of  personal  opinion,  and  even  in  one  man's  mind  it  might 
vary  materially  for  different  cases.  Under  ordinary  conditions,  the  speaker 
believes  that  a  single  clear  opening  twenty-five  (25)  per  cent  greater  than 
either  of  the  clear  openings  afforded  by  the  swing  type  will  give  equally 
good  or  better  facilities  for  navigation,  and  that  under  the  worst  possible 
conditions  the  excess  percentage  need  not  be  more  than  forty  (40).  Un- 
fortunately, though,  neither  the  speaker  nor  the  designer  of  the  bridge 
under  consideration  has  anything  to  say  about  deciding  this  point,  be- 
cause the  court  of  last  appeal  is  always  the  War  Department.  If  that 
department  deems  that  the  clear  opening  or  openings  suggested  by  the 
designer  be  insufficient,  it  has  no  hesitation  whatsoever  in  saying  so  and 

37 


in  compelling  the  petitioner  for  approval  to  increase  the  said  clear  open- 
ing or  openings  as  much  as  its  engineers  consider  advisable.  Up  to  the 
present  time  the  War  Department  has  almost  always  accepted  plans  of  the 
speaker's  in  which  the  excess  percentage  referred  to  has  been  twenty-five 
or  even  less;  but  its  having  done  so  in  the  past  is  no  reason  for  assuming 
that  its  engineers  will  always  be  willing  to  recognize  that  percentage  as 
their  maximum  requirement.  Accepting  this  settlement  of  the  question 
as  fixed,  it  is  practicable  to  compare  swing  spans  with  bascules  and  vertical 
lifts. 

In  most  cases  when  swing  spans  and  bascules  are  compared,  the  result  is 
either  a  stand-off  or  more  or  less  in  favor  of  the  bascule.  The  conditions 
would  be  unusual  where  the  swing  proves  to  be  much  more  economic — for 
instance,  where  the  deck  is  very  close  to  the  water,  thus  necessitating  a 
well  or  wells  for  receiving  the  counterweighted  end  or  ends  of  the  bascule. 
In  almost  no  practicable  case  is  the  swing  materially  more  economic 
than  the  vertical  lift,  unless,  perchance,  the  opening  be  very  narrow,  the 
vertical  clearance  very  great,  and  the  depth  of  the  bed  rock  small — a 
most  unusual  combination.  In  almost  every  case  of  comparison  which 
has  occurred  in  the  speaker's  practice  the  vertical  lift  has  proved  less 
expensive  than  the  rotating  draw. 

Considering  now  bascules  and  vertical  lifts,  in  most  cases  the  economic 
comparison  favors  the  latter  type.  It  always  does  so  if  the  vertical  clear- 
ance is  not  in  excess  of  fifty  or  sixty  feet.  If  the  clearance  be  the  usual 
one  for  ocean-going  vessels, — viz.,  135  feet,  the  cost  of  the  bascule  and  that 
of  the  vertical  lift  will  be  equal  for  clear  openings  of  about  one  hundred 
feet  or,  in  extreme  cases,  one  hundred  and  twenty-five  feet.  The  longer 
the  movable  span,  the  closer  the  deck  to  the  water,  the  deeper  the  bed- 
rock, or  the  smaller  the  required  vertical  clearance,  the  greater  will  be 
the  comparative  economy  of  the  vertical  lift. 

As  before  indicated,  the  treatment  of  the  economics  of  bridge  designing 
has  been  made  much  more  elaborate  and  exhaustive  than  that  of  any 
other  specialty.  For  this  there  are  four  reasons, — viz. : 

FIRST.  It  is  in  the  lead  alphabetically  on  the  list  of  specialties  dis- 
cussed. 

SECOND.  The  science  of  bridge  design  has  been  more  deeply  and  sys- 
tematically studied  than  that  of  any  other  branch  of  engineering. 

THIRD.  It  is  deemed  advisable  to  give  an  example  of  the  thorough 
treatment  of  economics  in  at  least  one  engineering  specialty. 

FOURTH.  Bridge  engineering  is  the  one  specialty  for  which  the  speaker 
feels  capable  of  writing  a  truly  exhaustive  treatment  of  the  question  of 
economics. 

For  these  reasons  he  trusts  that  his  hearers  will  pardon  him  for  taking 
so  much  time  for  the  detailed  discussion  of  "bridge  economics". 


LECTURE  III 

CITY  PLANNING* 

The  salient  feature  of  economics  in  design  and  construction,  so  far  as 
engineering  is  applied  to  city  planning,  may  be  said  to  lie  (as  in  other 
engineering  work)  in  a  more  or  less  accurate  adaptation  to  purpose.  In  city 
planning,  the  engineer  endeavors  to  determine,  for  example,  the  width 
which  any  street  ought  to  have,  so  that  it  shall  not  wastefully  be  made 
wider  than  necessary,  nor,  on  the  other  hand,  shall  it  prove  too  narrow 
to  perform  properly  the  traffic  function  which  pertains  to  it.  He  deter- 
mines whether  it  shall  be  a  traffic  artery,  a  secondary  street,  or  a  purely 
domestic  street.  In  so  doing  he  is  able  to  determine  not  merely  its  proper 
width,  but  also  the  strength  and  the  character  of  the  pavement  it  should 
have,  and  the  relative  allotment  of  space  to  roadway,  sidewalks,  etc. 

The  districting  of  the  city  for  different  uses,  the  control  of  building 
heights,  and  many  other  phases  of  city  planning  that  have  as  their  ulti- 
mate object  the  possibility  of  greater  adaptation  to  purpose,  are  economic 
considerations,  which  often  are  of  paramount  importance. 

DAMsf 

The  following  are  some  of  the  salient  economic  questions  in  the  design- 
ing and  building  of  dams: 

Should  dams  be  of  earth  or  masonry? 

If  of  earth,  should  there  be  a  concrete,  a  puddle,  or  a  soil  core,  or  none? 
What  slopes  should  be  used  on  upstream  and  downstream  faces?  What 
pavement  or  other  protection  on  the  slopes?  How  should  the  earth  be 
compacted? 

If  of  masonry,  should  the  dam  be  curved  in  plan  or  straight?  This  will 
depend  upon  the  nature  of  the  site,  the  length  of  structure,  and  other 
numerous  conditions.  Should  it  be  of  concrete,  or  cyclopean,  or  rubble? 
Should  it  be  massive, — i.e.,  solid  construction,  or  of  the  reinforced,  hollow 
type?  If  of  concrete  or  cyclopean  masonry  of  the  solid  type,  should  it  be 
built  in  forms  or  faced  with  pre-cast  concrete  blocks,  or  faced  with  stone? 
What  margin  of  safety  should  be  provided?  This  will  depend  upon  the 
importance  of  the  water  impounded  by  the  dam,  the  risk  to  life  and 
property  below,  and  the  available  funds,  as  well  as  other  considerations. 

All  these  are  economic  features  of  importance  that  affect  the  designing 
and  construction  of  dams. 

ELECTRIC  RAILWAYS 

In  the  "Proceedings  of  the  Engineers'  Club  of  Philadelphia"  for  July, 
1914,  there  is  a  paper  by  E.  P.  Roberts,  Esq.,  C.  E.,  entitled  "Reporting 
on  Public  Service  Properties",  in  which  is  treated  in  great  detail  the  sub- 
ject of  the  economics  of  electric  railways.  As  no  better  presentation 

*Data  furnished  by  Chas.  Mulford  Robinson,  Esq.,  C.  E.,  professor  of  civic  design 

in  the  University  of  Illinois. 
tData  furnished  by    Alfred  D.  Flinn,  Esq.,  C.  E.,  deputy  chief  engineer   of   the 

Board  of  Water  Supply  of  New  York  City. 

39 


thereof  could  well  be  made,  that  portion  of  the  paper  relating  to  the  said 
subject,  is  reproduced  nearly  verbatim  as  follows: 

General  Survey 

First,  obtain  a  bird's  eye  view  of  the  territory.  To  secure  this,  make 
a  preliminary  study  of  all  available  maps,  including  topographical,  and 
note  the  general  location  of  the  proposed  road,  the  location  of  the  terri- 
tory which  apparently  might  be  served,  and  such  factors  as  might  seem 
until  definite  information  is  obtained,  to  restrict  or  to  enlarge  the  territory 
served,  to  a  greater  degree  than  would  be  the  case  if  it  were  based  upon 
a  strip  two  or  three  miles  on  each  side  of  the  road.  An  arbitrary  assump- 
tion of  uniform  width  of  territory  served  is  misleading.  Location  of  rivers 
paralleling  the  route,  high  ridges  or  hills  near  the  right-of-way,  other 
railroads,  either  paralleling  or  at  an  angle  to  the  proposed  road,  and  other 
physical  and  transportation  features — all  affect  the  ease  of  access  to  the 
road,  the  traffic  which  should  be  secured,  and  the  service  which  should  be 
offered. 

Industrial  Developments 

Having  in  mind  a  possible  general  location,  then  some  preliminary 
knowledge  of  the  characteristics  of  the  territory  is  helpful  before  going 
over  the  route. 

What  is  the  general  character  of  the  industries?  Why  did  they  develop? 
Upward  or  downward  tendencies?  What  probable  future?  Can  the 
proposed  road  help  the  development? 

Mining — fluctuating  in  value  to  an  electric  road. 

Manufacturing — less  fluctuating  in  value  to  an  electric  road,  but  unless 
diversified,  quite  variable. 

Agricultural — usually  less  tendency  to  fluctuation,  but  depends  some- 
what upon  nationality  of  farmers;  generally  a  farming  community  spends 
less  money  for  unnecessary  riding  than  does  a  mining  or  a  manufacturing 
community. 

Study  census  reports  showing  growth  (or  decrease)  of  population. 
School,  voting,  and  other  records  stating  population,  etc.,  can  be  studied 
later. 

Note  the  characteristics  and  the  tendencies  of  growth  of  the  principal 
terminus. 

Of  secondary  terminus. 

Of  intermediate  territory. 

Note  direction  of  existing  railroad  traffic.  Why  have  the  roads  such 
directional  location?  Existing  business  and  social  relations  have  built 
up  a  certain  direction  of  travel;  and  if  the  proposed  road  does  not  serve 
such  existing  traffic  tendency,  what  reasons  are  there  for  presuming  that 
the  direction  of  movement  can  be  changed?  Make  note  of  this  to  ascertain 
more  accurately  later.  It  requires  exceptional  conditions  to  deflect 
existing  directions  of  travel. 

The  location  of  an  existing  road  may  have  resulted  from  either  through 
or  local  traffic  conditions.  If  the  former,  and  local  conditions  make  a 
cross-country  road  desirable,  then  the  traffic  condition  for  the  proposed 

40 


road  may  be  excellent,  but,  in  this,  as  in  every  other  matter,  all  state- 
ments must  be  carefully  weighed,  and  the  facts  must  be  ascertained  by 
investigation. 

Inspection  Of  Route  And  Territory 

Being  now  prepared  to  appreciate  what  is  seen,  a  rapid  trip  over  the 
route  is  advisable,  but  not  giving  too  much  attention  to  detail,  and  not 
reaching  definite  decisions.  It  will  be  time  enough  later  to  consider  the 
equivalent  of  5-ft.  contour  lines:  50-ft.  ones  are  sufficient  at  this  stage. 
During  such  a  trip,  intelligent  and  applicable  questions  can  be  asked,  and 
the  answers  recorded,  but  not  necessarily  digested  (and  certainly  not 
evaluated)  until  later.  Frequently,  printed  forms  can  be  left  with  bankers, 
secretaries  of  chambers  of  commerce,  etc.,  to  be  filled  in  and  mailed,  or, 
preferably,  collected  and  discussed  on  a  return  trip. 

A  return  trip  can  next  be  made  and  somewhat  more  leisurely,  and 
giving  more  attention  to  details,  topography,  character  of  soil,  width  of 
rivers,  heights  of  banks  and  of  high  water,  character  and  growth  of  indus- 
tries, crops  (gross  and  per  acre) ;  also  probable  effect  of  the  proposed  road 
on  the  character  of  crops,  present  routing  and  market,  population,  growth, 
and  characteristics.  Industrial  and  sociological  information  of  all  kinds, 
bank  reports,  building  loan  reports,  etc.,  all  are  important.  In  each  case 
comparative  statistics  extending  over  a  period  of  years  should  be  obtained 
— tendencies  and  direction  of  growth,  and  especially  of  decay,  should  be 
noted  and  the  reason  ascertained. 

Present  traffic  and  reason  for  traffic  should  be  noted.  How  much  of 
the  existing  traffic  will  the  proposed  road  obtain?  Probably  little,  if  any, 
of  such  traffic  as  originates  or  terminates  beyond  its  terminals — probably 
a  large  part  of  that  which  is  local  between  such  terminals. 

From  information  as  to  amount  and  direction  of  traffic  and  knowledge 
of  general  conditions  affecting  cost  of  construction,  and  having  considered 
strategic  position,  then  a  tentative  location  can  be  considered.  If  the 
country  is  rather  rough,  a  survey  of  one  or  more  routes  may  be  advisable; 
if  it  is  comparatively  level,  the  survey  may  be  postponed.  When  to  make 
survey  depends  on  the  time  available,  the  season  of  the  year,  and  other 
factors,  including  the  advisability  of  appearing  to  be  busy,  and  of  survey- 
ing more  than  one  route  in  order  to  obtain  interest  and  competition. 
This  is  about  the  only  time  when  anything  will  be  "given"  to  the  road. 

Tentative  Plan 

The  tentative  plan  will  be  based  on  such  ruling  and  maximum  grades 
as  the  engineer's  experience  indicates  to  him  will  probably  prove,  after 
further  examination,  to  be  about  right,  considering  the  magnitude  and 
direction  of  traffic,  topography,  etc.  Carried  along  with  consideration 
of  locations,  grades,  etc.,  will  be  preliminary  studies  of  the  equipment 
which  will  be  necessary  to  handle  the  traffic,  of  the  character  of  service 
best  fitted  to  the  conditions,  and  of  the  general  type  of  equipment  best 
suited  to  the  service  to  be  given. 

Tentative  train  sheets  should  be  prepared,  and  the  comparative  advan- 
tages and  disadvantages  tabulated.  Effect  on  platform  charges  (exceed- 

41 


ingly  important),  effect  on  total  and  maximum  peak  power  (as  to  each 
substation  and  as  to  power  house),  location  of  passing  points,  relation  of 
the  same  to  grade,  meeting  at  central  points  in  town,  and  whether  ad- 
visable or  not,  and  other  items  should  be  duly  considered. 

The  location  of  power  house  and  sub-stations,  of  car  shops,  etc.,  re- 
quires careful  consideration. 

The  business  probably  obtainable  for  each  class  of  service — passenger, 
express,  freight,  mail — should  be  estimated  on  an  annual  basis,  and  also 
monthly.  In  some  cases,  the  sale  of  power  and  light  may  be  contemplated, 
but  these  items  should  be  separated  from  receipts  from  railroad  operation. 
The  probable  rates  obtainable,  the  expense  of  operation,  including  finan- 
cial and  all  charges,  the  total  investment  and  the  net  income  for  the 
second,  fifth,  and  tenth  years  of  operation  (or  some  other  future  periods) 
must  be  predetermined  with  the  greatest  care. 

Modification 

The  next  step  is  to  consider  each  general  feature  and  then  each  detail 
of  each  general  class  and  ascertain  what  changes  could  be  made,  and  the 
net  result, — i.  e.,  the  effect  on  dividend. 

Affecting  Factors 

A  careful  study  should  be  made  of  the  past  history,  the  present  develop- 
ment, and  the  tendencies  of  the  territory;  and  these  should  be  considered 
with  reference  to  the  probable  effect  on  the  magnitude  and  the  character 
of  future  growth. 

The  rules  and  the  apparent  tendencies  of  the  decisions  of  the  Interstate 
Commission  and  of  the  Public  Service  Commission  having  jurisdiction 
should  be  investigated. 

Not  only  should  location,  construction,  and  equipment  be  considered 
with  reference  to  the  traffic  "in  sight",  but  also  with  reference  to  the 
development  of  the  territory,  including  the  possibility  of  assisting  in  such 
development;  and,  in  the  latter  connection,  the  character  of  construction 
and  of  equipment  which  will  be  most  desirable  if  such  development  is 
obtained. 

The  history  of  the  existing  transportation  companies  serving  the  same 
territory  should  be  noted,  also  the  policies  or  tendencies  of  the  officers, 
as,  for  example,  whether  they  have  fought  or  cooperated  with  other  electric 
railroads  along  their  lines. 

Profit  Or  Loss 

Profit  or  loss  depends  upon  the  difference  between  two  almost  equal  amounts. 

A  very  small  percentage  of  difference  in  receipts  or  expenses  will  make 
a  large  percentage  difference  in  the  amount  available  for  dividends. 

Location,  including  terminal  facilities,  will  largely  affect  the  gross 
income  and  also  the  cost  of  construction.  The  character  of  construction 
and  equipment  somewhat  affects  the  receipts,  and  largely  affects  the 
operating  expense,  including  maintenance,  depreciation,  and  accidents. 

Importance  Of  Careful  Preliminary  Investigation 
A  slight  change  in  location  may  favorably  or  unfavorably  affect  con- 

42 


structi on-cost  and  gross  and  net  income,  therefore,  practically  speaking, 
it  is  impossible  to  give  too  much  time  and  expense  to  a  careful  preliminary 
investigation. 

The  latter  will  frequently  indicate  that,  as  to  the  immediate  future, 
certain  locations  will  cost  a  comparatively  small  amount,  and  that  such 
grades  as  are  economically  advisable  for  the  traffic  immediately  in  sight 
can  be  constructed  at  slight  expense,  also  that  there  will  be  a  minimum 
expenditure  for  bridges  and  an  avoidance  of  grade  crossings  of  other 
railroads  or  of  highways.  It  may  be  possible  that  such  a  location  is  also 
advisable  as  to  the  more  distant  future,  including  strategical  position 
with  reference  to  business  competition.  If  the  grades,  bridges,  and  trestles 
can  be  so  modified  later  as  then  to  obtain  a  road  having  grades  desirable 
for  such  future  traffic,  the  location  may  be  advisable.  Probably,  how- 
ever, such  will  not  be  the  case  as  to  at  least  a  portion  of  the  route;  and  the 
future  must  always  be  considered. 

The  Future 

Considering  the  future  is  not,  however,  equivalent  to  building  for  the  future. 
Planning  for  the  future  is  advisable,  but  expending  capital  in  order  to 
provide  for  the  distant  future  requires  careful  consideration.  It  might 
be  better  to  place  such  money  in  a  sinking  fund,  rather  than  in  unpro- 
ductive construction.  Such  sinking  fund  is  usually  a  theoretical  con- 
sideration. The  more  usual  consideration  is,  "Can  such  present  unneces- 
sary expenditure  be  saved  and  the  total  cost  reduced,  and  thereby  the 
proposition  be  made  more  attractive  to  capital?"  Steel  bridges  vs. 
wooden  trestles  are  simple  examples  of  such  consideration.  Future 
changes  of  grade  will  require  (at  least  usually)  a  greater  total  expenditure 
than  if  the  roadbed  were  originally  constructed  at  such  final  grade,  but, 
nevertheless,  the  interest  saved  is  always  important  and  may  be  vital. 

Change  in  location  is  always  expensive.  When  the  road  is  proposed, 
much  of  the  right-of-way  has  little  value;  and  a  skillful  promoter  can 
sometimes  obtain  right-of-way  in  a  new  territory  for  a  comparatively 
small  amount.  When,  however,  the  road  develops  the  territory,  then 
land  becomes  worth  more  to  the  owner,  and  is  likely  to  cost  the  railroads 
on  the  basis  of  even  a  greater  percentage  of  increase. 

The  general  result  is  that,  to  a  considerable  degree,  the  design  and  more 
especially  the  construction  which  make  provision  for  the  future  should  be 
mainly  in  connection  with  such  items  as  will  require  a  far  greater  total 
expenditure  when  in  the  future  the  same  are  modified  or  reconstructed 
than  if  originally  so  constructed.  Right-of-way,  and  especially  terminal 
facilities,  are  free  from  maintenance  and  depreciation;  and  to  change  or 
add  to  them  in  the  future  is  very  costly.  On  the  other  hand,  such  items 
as  ties,  poles,  trestles,  minor  buildings,  and  rolling  stock,  require  renewal 
in  a  comparatively  few  years  and  are  largely  independent  as  to  their 
functions.  Usually  they  should  be  designed  with  reference  to  the  near 
future;  and  the  character  of  replacement  should  be  allowed  to  await  the 
development  of  the  business. 

System  And  Data  Sheets 
When  making  a  preliminary  investigation  of  the  territory,  a  definite 

43 


plan  should  be  followed.  Doubtless  all  engineers  who  are  experienced  in 
such  matters  prepare  data  sheets  on  which  they  note  such  things  as  they 
consider  important.  It  is  very  advisable  to  prepare  general  data  sheets, 
tabular  forms,  etc.,  at  times  of  comparative  leisure.  When  a  specific 
case  is  under  consideration,  the  forms  prepared  are  liable  to  be  affected 
by  special  conditions  and  thereby  lose  general  applicability  and  con- 
venience for  comparison. 

The  general  character  of  information  desired  can  be  divided  into  two 
classes: 

First.  That  which  in  a  general  way  always  exists.  For  example:  division 
of  territory  into  cities,  towns,  villages,  rural,  etc.;  population  and  its 
tendencies;  public  buildings;  public  service  properties  operated  by  the 
city  or  by  corporations;  educational  institutions;  churches;  theatres; 
libraries;  parks;  fair  grounds;  banks  and  building  and  loan  associations; 
manufacturing  establishments;  wholesale  and  retail  business  houses;  etc. 

Second.  Conditions  of  an  unusual  character,  such  as  oil  or  gas  wells, 
exceptionally  large  state  institutions,  manufacturing  plants  with  world- 
wide reputation  and  having  many  employees,  etc. 

The  unskilled  observer,  and  sometimes  even  the  skilled  observer 
occasionally  neglects  to  check  off  his  list;  and  he  obtains  quite  complete 
information  relative  to  the  unusual  or  striking  and  spectacular  conditions 
and  omits  some  of  the  items  in  the  first  class.  The  result  is  that  additional 
money  and  time  are  required  in  order  to  obtain  data,  or  else  they  are  not 
obtained. 

Data 

When  obtaining  data  from  individuals,  considerable  allowance  must  be 
made.  It  is  well  known  that  locating  the  high-water  mark  of  a  stream  on 
the  basis  of  the  statement  of  the  "oldest  inhabitant"  is  very  unwise. 
Usually,  information  can  be  obtained  from  more  than  one  source  and  the 
advisable  discount  made;  and  thereby  fairly  accurate  information  can  be 
obtained  as  to  practically  all  of  the  major  non-technical  factors  relative 
to  the  territory.  Bank  statements  and  talks  with  bankers  are  very  helpful. 
The  country  banker  has  a  detailed  knowledge  of  the  crops,  mortgages, 
and  points  to  which  shipments  are  made,  and  as  to  all  of  the  activities  of 
the  rural  communities;  and  his  statement  can  be  accepted  as  approxi- 
mately accurate,  especially  if  checked  up  in  a  few  cases  by  the  examination 
of  farms,  etc.  The  conditions  of  the  fences,  buildings,  &c.,  usually  in- 
dicate the  facts  as  to  mortgages. 

The  application  of  general  statistics  to  a  specific  case  may  be  helpful; 
but  it  is  always  accompanied  by  the  serious  danger  that  figures  may  be 
used  which  should  not  be  applied  to  the  case  under  consideration. 

Statistics  can  be  obtained  as  to  roads  in  the  same  general  territory, 
and  possibly  having  the  same  principal  terminal  town;  and  these  should 
be  considered  carefully.  No  statistics  from  any  road  should  be  applied 
to  the  proposed  road,  unless  the  engineer  has  quite  complete  knowledge 
as  to  the  road  from  which  the  figures  were  obtained.  No  two  roads  are 
exactly  alike,  and,  as  before  stated,  it  must  never  be  forgotten  that  a  very 
slight  difference  in  the  net  receipts  may  make  the  difference  between 
profit  or  loss  to  the  stockholders. 

44 


ENGINEERING  TEACHING* 

This  is  a  subject  concerning  which  the  economics  are  difficult  to  define. 
Dr.  Swain  outlines  them  thus: 

1.  Engineering  teaching  should  be  done  by  men  who  have  had  prac- 
tical experience,  and  also  who  have  had  some  training  in  teaching  and 
psychology  and  who  are  in  sympathy  with  the  point  of  view  of  young 
men.    Moreover,  and  most  important  of  all,  they  should  be  well-balanced 
men,  and  not  faddists.    I  am  inclined  to  think  that  the  teaching  profession, 
as  a  whole,  contains  more  faddists  and  men  of  unbalanced  views  than  does 
any  other  occupation;  and  I  consider  that  the  teacher  can  do  more  for 
his  pupils  by  giving  them  sane  and  sensible  points  of  view,  methods  of 
attack,  and  clear  conception  of  the  possibilities  of  the  subject  studied  and 
its  relation  to  other  subjects,  than  by  filling  them  up  with  technical 
knowledge. 

2.  The  teacher  should  aim  first  of  all  to  teach  his  students  to  think 
logically,  clearly,  and  concisely.     The  great  bane  of  teaching  today  is 
that  its  object,  in  most  cases,  appears  to  be  to  give  information.    The 
result  is  that  it  makes  rule-of-thumb  men.     Many  students,  however, 
seem  to  think  that  that  kind  of  thing  is  what  they  come  to  school  to  get; 
and  it  takes  some  readjustment  of  their  point  of  view  to  make  them  see 
that  what  they  need  more  than  anything  else  is  clear  thinking.    For  this 
reason,  what  a  man  gets  out  of  his  college  will  depend  more  upon  the  teach- 
ers with  whom  he  comes  in  intimate  contact  than  upon  the  subjects 
which  he  studies. 

3.  Engineering  teaching  should   consist   of  courses   which   are  well 
coordinated,  so  that  there  shall  be  a  gradual  and  systematic  advance  from 
one  subject  to  another,  without  any  more  repetition  than  is  necessary  to 
hammer  the  principles  in.     Some  amount  of  repetition  is  desirable  for 
this  purpose.    One  of  the  most  difficult  things  is  to  procure  the  proper 
coordination  between  engineering  topics  taught  by  the  engineering  depart- 
ment,  and  other  subjects,  like  mathematics,  physics,  etc.,  which  are 
taught  by  other  departments. 

HARBORsf 

It  is  somewhat  difficult  to  generalize  upon  the  economics  of  harbor 
construction,  because  every  harbor  has  its  own  problems  to  solve,  depend- 
ing on  class  and  quantity  of  freight  and  shipping,  of  railway  approaches, 
of  climate,  and  of  a  dozen  other  contingencies. 

It  may,  however,  be  premised  that  there  is  a  solution  for  each  individual 
case,  and  that  the  economic  development  in  any  case  must  be  found  in  a 
thorough  consideration  of  conditions.  Such  conditions  in  nearly  every 
instance  will  be  found  to  be  rapidly  changing  with  increases  in  size  and 
draught  of  ships,  necessitating  longer  docks  and  more  commodious  freight 
storage.  In  Canada,  especially,  the  very  great  increase  in  ocean  freights, 
demanded  by  the  immense  shipments  of  wheat  from  the  Northwest,  has 

*Data  furnished  by  Dr.  Geo.  F.  Swain,  professor  of  civil  engineering  at  Harvard 
University,  and  consulting  engineer,  also  Past  President  of  the  American 
Society  of  Civil  Engineers. 

tData  furnished  by  Col.  Wm.  P.  Anderson,  chief  engineer  of  the  Marine  and  Fish- 
eries Department  of  Canada,  and  Past  President  of  the  Canadian  Society  of 
Civil  Engineers. 

45 


forced  in  Canadian  ports  rapid  and  vast  increases  in  harbor  accommo- 
dation— instance  the  ports  of  Vancouver,  Prince  Rupert,  Port  Arthur, 
Fort  William,  Montreal,  Quebec,  Halifax,  and  St.  John. 

For  the  economical  and  successful  development  of  a  harbor,  the  first 
essential  is  a  comprehensive  layout  of  the  water-front  as  a  whole,  taking 
advantage  of  all  local  factors,  such  as  contour  of  shore,  depth  of  water, 
set  of  current,  facility  of  railway  approach,  in  order  to  secure  the  best 
results.  It  may  be  laid  down  as  a  general  rule  that  the  best  layout  is  to 
provide  wharves  in  parallel  lines,  at  such  an  angle  to  the  quay  wall  as  will 
allow  easy  railway  approach  and  facilitate  the  entry  of  vessels  to  the  docks. 

In  most  harbors,  sufficient  provision  has  not  been  made  in  advance  for 
progressive  deepening,  and  much  waste  has  ensued  in  consequence  of  the 
necessity  of  rebuilding  for  each  increase  in  depth  demanded  by  the  deeper- 
draught  vessels. 

The  question  of  building  wharves  of  timber  or  of  more  permanent 
material  is  one  that  gives  much  thought  to  the  engineer,  and  the  decision 
must  depend  on  many  factors.  With  the  advance  in  cost  of  timber  and 
the  cheapening  of  concrete  processes  the  tendency  is  very  general  to  use 
concrete  increasingly.  It  is  often  found  to  be  good  practice  from  the 
score  of  economy  to  place  timberwork  cribs  below  low  tide  and  finish 
with  concrete  blocks  or  mass-concrete. 

There  are  many  problems  yet  to  be  solved  in  connection  with  the  com- 
position and  placing  of  concrete.  Many  instances  have  occurred  of  the 
disintegration  of  concrete  by  chemicals  absorbed  from  salt  water,  and  it 
is  also  a  question  whether  reinforcement  in  salt  water  is  not  liable  to 
corrosion.  There  is  plenty  of  room  for  further  study  of  all  these  problems. 
In  my  personal  experience  I  have  seen  a  good  deal  of  destruction  of  con- 
crete quay  walls,  the  bad  disposition  of  the  interior  filling  and  the  frost 
forcing  the  walls  out  of  alignment. 

Sufficient  consideration  has  in  the  past  not  been  given  to  convenience 
of  construction  of  freight  sheds  and  to  vehicle  and  rail  approach  and  for 
handling  freight.  Generally,  freight  sheds  should  be  so  designed  that 
machinery  can  be  used  for  loading  and  unloading  into  and  out  of  them; 
and  so  that  transfer  from  rail  to  ship  can  be  effected  with  the  least  possible 
handling  and  truckage.  The  best  means  of  accomplishing  such  aims  must, 
of  course,  vary  with  every  shed  and  with  every  class  of  freight. 

In  modern  harbors  it  is  invariably  a  rule  to  separate  rail  transport 
from  other  vehicle  transport  and  so  to  arrange  the  approaches  that  the 
one  class  cannot  interfere  with  the  other. 

HIGHWAYS* 

Concerning  the  economics  of  highway  designing  and  construction,  the 
following  data  are  taken  from  a  letter  of  W.  G.  Harger,  Esq.,  C.  E. 

The  details  of  economic  highway  design  are  everywhere  a  local  problem 
depending  on  the  available  materials,  climatic  conditions,  and  traffic  re- 
quirements. I  know  of  no  one  who  has  had  enough  personal  experience 
in  the  design,  construction,  and  maintenance  of  the  various  types  under 

*Data  fiirnished  by  W.  G.  Harger,  Esq.,  C.  E.,  engineer  of  the  Commission  of 
Highways  of  New  York  State. 

46 


different  sectional  requirements  to  pose  as  an  expert  over  any  extended 
part  of  the  country,  except  on  very  general  lines. 

The  salient  features  which  govern  the  cost  of  a  highway  system  are 
legislative  and  finance  programs  which  provide  the  necessary  money  at 
the  proper  time,  an  engineering  design  which  at  all  times  strives  to  use 
local  materials  to  advantage,  and  a  constructing  staff  which  insists  on 
good  workmanship. 

The  financing  of  our  New  York  State  system  of  highways  has  never 
been  well  worked  out  for  either  construction  or  maintenance;  and  what 
applies  to  us,  I  believe,  is  true  of  a  large  percentage  of  cases.  The  per- 
manent features  of  a  highway  improvement  are  the  grading,  drainage, 
and  foundation.  The  surfacing  is  temporary,  even  for  the  so-called 
"permanent"  types.  Road  improvements  are  generally  financed  by  long- 
term  bonds;  and  no  provision  is  made  for  construction  renewals  before 
the  original  bonds  expire.  The  rigid-pavement  types  such  as  brick, 
asphalt,  concrete,  etc.,  need  resurfacing  in  from  ten  to  twenty  years;  the 
macadams  in  from  five  to  ten  years.  The  ordinary  maintenance  for  the 
rigid  types  will  run  about  $200  per  mile  per  year  with  a  resurfacing  charge 
of  $10,000  to  $15,000  per  mile  at  intervals  of  about  15  years.  The  ordinary 
maintenance  on  macadams  is  about  $500  per  mile  per  year,  with  a  re- 
surfacing charge  of  $4,000  to  $6,000  per  mile  at  intervals  of  seven  to 
eight  years.  The  yearly  cost  of  maintenance  and  renewals  amounts  to 
approximately  $1,000  per  mile.  Provision  for  this  amount  has  never  been 
made,  which  circumstance  results  in  a  gradual  deterioration  of  the  roads, 
and  will  finally  occasion  an  unnecessarily  large  expenditure  to  put  the 
system  back  in  good  condition.  Proper  provision  should  be  made  for 
maintenance  and  renewal,  or  else  a  large  future  waste  is  certain  to  occur. 
A  foresighted  policy  in  this  particular  would  save  the  community  more 
than  would  any  engineering  economics  of  the  design. 

The  engineering  design  rests  on  the  consideration  of  construction, 
maintenance,  and  renewal  costs.  In  discussing  this  problem  most  of 
the  current  literature  and  most  highway  speakers  emphasize  and  confine 
economics  to  the  selection  of  pavement  type.  This  is  a  natural  result  of 
the  exploitation  of  various  materials  and  patented  processes.  As  a  matter 
of  fact,  our  experience  indicates  that,  for  75  to  80  per  cent  of  the  roads, 
the  final  cost  is  not  greatly  affected  by  the  selection  of  type,  except  as  it 
governs  the  use  of  local  material.  In  general,  the  high  and  the  low  priced 
pavements  cost  about  the  same,  considering  interest  on  first  cost,  main- 
tenance, and  renewals.  What  is  saved  on  first  cost  is  spent  on  maintenance. 

The  engineering  economics  of  design  are  limited  to  a  careful  grading 
and  safe  foundation  design,  utilizing  local  material;  and  to  a  selection  of 
the  cheapest  first-cost  type  of  pavement  of  the  general  class  required  by 
the  traffic, — i.  e.,  a  rigid  type  for  very  heavy  traffic,  and  for  all  ordinary 
roads  any  type  which  will  utilize  local  materials  to  their  best  advantage. 
On  from  75  to  80  per  cent  of  the  mileage  of  most  State  systems,  any 
standard  type  of  construction  which  is  the  cheapest  in  first  cost  will  gen- 
erally be  the  cheapest  in  the  end. 

The  inspection  of  construction  has  more  effect  on  the  final  cost  than 
has  the  design.  On  government  work  there  is  a  great  variation  in  the  care 

47 


and  knowledge  of  the  inspectors.    Well-built  macadams  are  much  cheaper 
in  the  end  than  poorly  constructed  brick  or  concrete  pavements. 

The  problem  of  improving  inspection  is  a  difficult  one,  and  the  results 
appear  to  be  spasmodic.  If  good  inspection  is  not  reasonably  certain,  the 
more-nearly-"  fool-proof "  macadams  are  the  most  economical  designs. 

INSPECTION* 

Engineering  inspection  has  two  economic  relations,  first  in  its  effect 
upon  the  work  inspected,  and  second  in  the  actual  conduct  of  the  in- 
spection. 

It  is  inevitable  that  errors  occur  in  the  manufacture  of  materials  and 
in  construction,  irrespective  of  the  question  of  intentional  avoidance  of 
the  requirements  of  the  specifications.  The  later  the  discovery  of  such 
errors  in  the  progress  of  engineering  work  the  more  expensive  is  the  cor- 
rection, both  in  its  own  cost  and  in  the  cost  of  delay  to  the  completion 
of  the  work.  It  is,  therefore,  of  prime  importance  that  the  manufacture 
of  material,  the  fabrication  in  the  shops,  and  the  erection  in  the  field  should 
have  all  errors  and  departures  from  the  specifications  discovered  and 
corrected  at  the  earliest  possible  moment.  Competent  inspection  serves 
not  only  to  discover  and  correct  such  errors  but  also  to  aid  the  contractor 
in  avoiding  them  and  to  lead  him  to  stronger  efforts  on  his  own  part,  when 
he  is  well  aware  that  such  errors  are  certain  to  be  discovered  and  the 
responsibility  brought  back  to  him.  Competent  inspection  can  also 
frequently  suggest  more  expeditious  or  economical  methods  of  manufac- 
ture and  thereby  tend  to  economy. 

The  performance  of  inspection  work  has  become  somewhat  of  a  specialty 
and  requires  experienced  and  skilled  men  of  a  number  so  located  as  to 
avoid,  as  far  as  may  be,  the  expense  of  travel  and  the  loss  of  time  necessary 
thereto.  When  the  manufacture  of  engineering  materials  for  a  contract 
is  conducted  at  a  number  of  different  points,  such  work  progresses  at 
approximately  the  same  time  and  must  be  inspected  by  a  number  of  men; 
the  manufacture  may  be  intermittant,  requiring  more  men  at  one  time 
than  at  another;  and  the  greatest  economy  is  accomplished  through  an 
organization  of  experienced  inspectors  who  are  able  to  undertake  the  work 
of  inspection  (each  at  his  location)  for  several  parties  at  the  same  time. 
With  such  an  organization  skillfully  handled,  there  is  a  minimum  amount 
of  lost  time  and  expense  in  traveling,  with  a  corresponding  reduction  of 
cost. 

The  processes  of  manufacture  of  material  are  so  highly  developed  that 
large  output  with  minimum  handling  and  delay  is  essential  to  the  success- 
ful operation  of  the  manufacturing  plant.  Properly  to  conduct  the  in- 
spection under  these  conditions,  it  is  essential  that  the  inspectors  be  ex- 
perienced not  only  in  the  line  of  work  but  also  frequently  with  the  indi- 
vidual manufacturer's  facilities  and  methods.  The  inspector  must  have 
full  knowledge  of  all  details  of  manufacture  and  must  know  by  previous 
experience  when  his  presence  at  any  portion  of  the  works  is  essential  to 
the  best  carrying  out  of  his  inspection. 

*Data  furnished  by  P.  S.  Hildreth,  Esq.,  C.  E.,  of  Hildreth  &  Co.,  inspecting 
engineers,  New  York  City. 

48 


The  above  remarks  apply  particularly  to  important  engineering  struc- 
tures such  as  bridges,  steel  frames  of  large  buildings,  important  machinery, 
and  the  like.  No  branch  of  engineering  requires  more  of  the  old-fashioned 
quality  of  common  sense  and  tact,  thoroughness,  and  loyalty  to  the  work 
than  does  inspection.  At  best  it  cannot  be  entirely  complete,  nor  can  it 
replace  the  requirement  of  contracts  and  specifications  as  to  the  essential 
qualities  of  materials  and  workmanship;  but  it  can  always,  if  well  done, 
be  of  marked  economic  value  in  connection  with  the  work  itself — and 
frequently  to  the  contractor. 

MINING* 

The  business  of  mining  consists  in  the  extraction  of  valuable  minerals 
from  the  earth  with  the  greatest  possible  profit.  Like  Gaul  it  is  divided 
into  three  parts. 

1.  Exploration  or  prospecting.    The  search  for  minerals. 

2.  Extraction  of  the  ore  from  the  ground. 

3.  Reduction  of  the  mineral  to  a  marketable  condition. 

With  the  exception  of  gold,  all  metals  and  minerals  mined  vary  in  value 
from  time  to  time;  and  mining  operations  should  be  adjusted  so  that  the 
maximum  profit  shall  be  obtained  during  a  period  of  high  prices.  Copper, 
lead,  zinc,  and  mercury  were  sold  in  1916  at  double  the  minimum  prices  of 
1914.  Other  minerals,  such  as  petroleum,  potash,  borax,  and  nitrates,  also 
vary  considerably  in  value  from  year  to  year. 

Exploration,  Prospecting,  Or  The  Search  For  Minerals 

Under  normal  conditions,  the  vast  majority  of  mineral  deposits  through- 
out the  world  are  of  too  low  grade  to  be  worked  profitably.  Under  any 
circumstances,  owing  to  the  fact  that  we  cannot  see  into  the  ground,  the 
work  of  prospecting  and  exploration  is  usually  fruitless  and  carried  on  at 
a  loss.  It  is  notorious  that  great  and  successful  mining  corporations 
(mining  copper,  lead,  or  oil)  spend  very  little  of  their  funds  on  exploration 
work  searching  for  minerals,  except  in  very  favorable  or  well-proven  dis- 
tricts. Such  companies  prefer  to  purchase  mineral  deposits,  even  though 
the  price  is  high,  after  their  discovery  by  other  parties.  This  is  a  better 
economic  policy  than  to  expend  funds  in  a  fruitless  search.  In  any  case, 
the  proportion  of  money  invested  in  exploring  for  mineral  deposits  should 
be  very  strictly  limited,  in  order  to  avoid  undue  risks  of  losing  the  capital 
invested. 

In  some  deposits,  such  as  coal,  salt,  iron,  and  sulphur,  these  risks  are 
not  always  so  great;  but,  ordinarily,  the  costs  incurred  in  searching  for 
deposits  of  gold,  silver,  copper,  and  lead  are  enormous. 

The  Extraction  Of  Mineral  From  The  Earth 

This  problem  is  that  of  finding  a  method  of  extracting  the  ore  at  the 
minimum  cost.  It  varies  enormously  with  the  size  of  the  deposit,  with 
its  character  and  geographical  location,  with  the  grade  of  the  ore,  and 
with  numerous  problems  of  administration,  such  as  drainage,  transpor-  |J 

*Data  furnished  by  James  W.  Malcolmson,  Esq.,  M.  E.,  consulting  engineer  to  the 
Lucky  Tiger-Combination  Gold  Mining  Company,  Kansas  City,  Mo.,  and 
Mexico. 

49 


tation,  ventilation,  and  other  factors.  Where  labor  is  high  in  price  and 
fuel  cheap,  as  in  the  United  States  and  European  countries,  labor  should 
be  economized  to  the  last  degree;  and  machinery,  explosives,  and  scientific 
method  of  transportation  should  be  utilized  to  the  greatest  possible  extent. 
In  other  countries  where  labor  is  cheap,  fuel  high-priced,  and  railroad 
facilities  poor,  a  different  policy  must  be  adopted;  as  money  may  readily 
be  lost  by  the  use  of  machinery,  especially  if  it  be  necessary  to  import 
skilled  labor  to  handle  the  equipment.  All  the  factors  in  the  problem  vary 
in  every  mining  field;  and  it  is  only  by  careful  study  that  the  proper 
economic  plan  of  operation  can  be  worked  out.  Conditions  in  Joplin, 
Missouri,  may  vary  so  greatly  from  those  in  Clifton,  Arizona,  or  in 
Alaska,  that  an  engineer  successful  in  one  of  these  fields  often  fails  utterly 
when  transferred  to  another  district.. 

The  mining  of  ore  occurring  in  thin  seams  and  worth  $100  or  $1,000  per 
ton  presents  difficulties  and  economic  problems  very  different  from  the 
mining  of  immense  deposits  of  copper  containing  values  of  $6  per  ton  or 
coal  worth  $1  per  ton.  The  extraction  of  oil  at  $1  per  barrel  or  gas  at 
1  or  2  cents  per  thousand  feet  presents  yet  another  class  of  economic 
problems  altogether  different  in  character,  although  the  underlying  main 
object  is  always  the  same — viz.,  to  earn  a  profit  on  the  investment,  and  the 
return  of  the  capital  invested  before  the  deposit  is  worked  out  and  ex- 
hausted. 

It  is  of  interest  to  consider  to  what  depths  mining  is  economically 
practicable. 

Coal  is  mined  in  Belgium  at  a  depth  of  4,000  feet.  Copper  is  mined  in 
Michigan  from  5,300  feet  in  depth,  and  gold  is  mined  in  the  Transvaal 
from  almost  as  great  a  depth.  The  problem  of  mining  from  great  depths 
is  altogether  an  economic  one,  the  difficulties  met,  the  costs  of  hoisting 
and  pumping,  the  problems  of  increasing  temperature  and  ventilation 
being  all  engineering  questions  for  solution. 

Mining  of  any  ore-deposit  is  a  transitory  business;  and,  by  the  time  the 
ore  is  exhausted,  the  work  ceases  and  the  mine  is  abandoned.  The  busi- 
ness, therefore,  has  special  economic  risks  to  such  an  extent  that  it  is 
generally  recognized  as  an  extra  hazardous  financial  operation,  and  is 
often  frowned  upon  by  so-called  conservative  capitalists.  At  the  same 
time  it  can  readily  be  demonstrated  that  the  whole  structure  of  our 
civilization  rests  on  the  mining  industry.  Without  coal,  iron,  copper, 
and  other  minerals  we  should  be  back  once  more  in  the  stone  age. 

Reduction  Of  The  Mineral  To  A  Marketable  Condition 

The  methods  of  reduction  vary  so  materially  with  the  different  ores 
and  the  different  localities  where  they  are  mined  that  it  would  be  almost 
impracticable  either  to  systematize  them  or  to  discuss  their  economics, 
hence  the  attempt  will  not  be  made.  Good  judgment  and  common  sense, 
applied  to  each  case  as  it  arises,  are  the  surest  means  of  attaining  an 
economic  method  of  reducing  and  concentrating  ores. 

50 


RAILROADING* 

The  subject  of  the  economics  of  modern  railroading  is  a  broad  and  in- 
tricate one,  and  deserves  a  full  and  elaborate  treatment  by  a  master  hand; 
but,  unfortunately,  none  of  the  authorities  seem  inclined  to  write  an 
exhaustive  treatise  on  the  subject.  Wellington's  great  work,  "The  Eco- 
comic  Theory  of  Railway  Location",  is  now  out  of  date,  and  should  be 
replaced  by  a  modern  book  covering  the  entire  ground. 

The  best  that  the  speaker  has  been  able  to  do  with  this  subject  for  these 
lectures  was  to  obtain  a  few  notes  on  railroad  economics  from  two  of  the 
highest  American  authorities;  and  these  are  presented  herewith. 

Mr.  Holbrook  writes:  Safety  of  the  road  and  of  trains  being  assured 
so  far  as  possible,  economy  is  of  prime  importance.  This  is  true  through- 
out all  the  departments  of  the  railroad  organization.  The  civil  engineer 
is  especially  concerned  with  the  economics  which  may  be  attained  by 
proper  care  in  location,  in  construction,  in  maintenance,  and  in  structures. 

The  location  problem  may  be  taken  as  typical. 

The  road  must  be  located  so  as  to  insure  that  net  earnings  shall  be  as 
large  as  possible.  To  do  this: —  (1)  Provide  for  the  maximum  possible 
income  by  running  the  line  to  or  through  all  important  traffic  points 
which  can  reasonably  be  reached.  (2)  Provide  for  the  smallest  possible 
expense  by  so  locating  the  line  that  the  sum  of  operating  expenses  and 
fixed  charges  shall  be  a  minimum.  ("Operating  expenses"  as  here  used 
include  all  expenses  for  operation  and  maintenance). 

The  procedure  recommended  by  Wellington,  which  is  probably  the 
safest  and  best,  is  to  lay  down  first  the  cheapest  line  which  will  carry  the 
traffic  with  safety.  This  will  be  a  relatively  expensive  line  to  operate, 
and,  probably,  will  not  be  the  best  (or  most  economical)  line,  but  the 
fixed  charges  for  interest  upon  the  construction  cost  will  be  small.  Then 
study  this  line  in  detail,  and  revise  it  only  where  the  revision  can  be 
shown  to  be  economical  in  itself,  reducing  grades  and  removing  more  or 
less  of  the  curvature,  distance,  and  rise  and  fall.  In  considering  the 
effects  of  these  changes  upon  operating  expenses,  it  is  necessary  to  take 
into  account  the  results  not  only  upon  the  cost  of  running  trains,  but  also 
upon  the  cost  of  maintaining  structures. 

By  reducing  the  ruling  grade  we  make  it  possible  to  handle  heavier 
trains,  and  therefore  fewer  trains  are  necessary.  This  results  in  a  saving 
(which  may  be  very  large)  in  operating  expenses. 

The  reduction  of  curvature,  distance,  and  rise  and  fall  is  of  less  financial 
importance;  but  the  effects  are  definite  and  of  sufficient  consequence  to 
warrant  most  careful  study  of  the  line,  section  by  section  and  part  by  part. 

The  effects  of  each  proposed  change  upon  construction-cost  and  upon 
operating-expenses  are  calculated,  and  the  interest  charge  upon  the  in- 
creased cost  of  construction  is  compared  with  the  annual  saving  in  cost 
of  operation.  So  for  each  of  the  proposed  changes. 

Other  items  enter  into  the  problem,  but  these  are  the  most  important. 


:Data  furnished  by  Elliot  Holbrook,  Esq.,  C.  E.,  valuation  expert  to  the  Union 
Pacific  Railway  System,  and  Fred  Lavis,  Esq.,  C.  E.,  consulting  engineer  to 
the  American  International  Corporation. 

51 


Construction  and  maintenance  problems  might  be  discussed  similarly. 
Many  of  the  problems  involved  are  not  special  to  railroad  work,  but  some 
of  them,  as  track,  signals,  etc.,  are  not  met  with  elsewhere. 

There  are  certain  special  questions  of  design  where,  as  always,  economic 
considerations  control;  as,  for  example,  in  determining  the  proper  size 
and  weight  of  rail  for  a  certain  line,  the  proper  size  and  material  for  ties, 
the  use  of  special  steels  in  track  work  (especially  in  frogs  and  switches), 
questions  involving  the  design  of  signal  systems,  the  placing  of  passing 
sidings  to  give  the  maximum  capacity  to  the  line  for  a  given  expenditure, 
the  design  of  yards  and  terminals,  etc. 

Mr.  Lavis  writes  thus:  A  railroad  is  a  machine,  the  product  of  which 
is  transportation.  The  type  of  machine  which  produces  the  finished 
article  at  lowest  cost  is  the  most  economical.  The  total  cost  of  transpor- 
tation is  composed  of  two  principal  factors,  the  actual  cost  of  operation 
and  the  interest  on  the  investment.  The  latter  is  governed,  of  course,  by 
the  original  cost  of  the  line  and  its  equipment.  The  cost  of  operation  is 
divided  into  four  principal  items:  General  expenses,  Traffic  expenses, 
Cost  of  transportation,  and  Cost  of  maintenance,  the  latter  two  being 
those  in  which  the  engineer  is  generally  most  interested.  The  Cost  of 
transportation  is  affected  by  Distance,  Curvature,  Rise  and  fall,  and  Rate 
of  ruling  gradient.  The  cheapest  line  to  operate  between  any  two  points 
is  a  straight  line  of  a  uniform  rate  of  gradient,  provided  this  latter  does 
not  exceed  the  reasonable  limits  of  economical  operation  by  adhesion 
locomotives. 

Deviation  from  a  straight  line  involves  greater  distance  and  introduces 
curvature,  both  of  which  increase  the  total  resistance  to  be  overcome  by 
the  locomotive,  and,  therefore,  increase  the  cost  of  operation.  Deviation 
from  a  uniform  gradient  introduces  rise  and  fall.  Within  certain  limits 
this  has  little  effect  on  the  cost  of  operation,  as  the  saving  in  power  on  the 
down-grades  offsets  the  additional  power  required  to  climb  the  up-grades; 
but  beyond  these  limits  the  stored  momentum  in  the  moving  train  is 
destroyed  by  the  use  of  brakes  on  the  descending  gradients,  and  the 
additional  climbs  are  added  resistance.  All  stops  increase  the  cost  of 
operation. 

The  rate  of  gradient  is  often  of  importance;  and  additional  distance 
may  be  justified  to  obtain  a  lower  rate.  The  value  of  this  item  depends 
largely  on  the  volume  and  the  kind  of  traffic;  but,  provided  the  amount 
of  the  rise  and  fall  is  the  same,  it  is  by  no  means  always  the  case  that  a 
lower  rate  of  gradient  permits  cheaper  operation,  if  it  involves  greater 
distance '(or  even  greatly  increased  cost  of  construction)  to  attain  it. 

A  further  item  of  importance  involves  the  positive  or  negative  values 
of  deviation  due  to  the  necessity  of  reaching  centres  of  traffic. 

The  costs  of  maintenance  depend  partly  on  the  natural  wear  and  tear 
due  to  the  action  of  the  elements,  which  affect  in  different  degrees  different 
types  of  structures, — that  is  to  say,  whether  they  are  of  wood,  stone,  or 
iron — and  partly  on  the  wear  and  tear  due  to  the  traffic  passing  over  the 
line,  which  amount  depends  on  the  volume  of  the  said  traffic. 

52 


SEWERAGE* 

Concerning  the  economics  of  his  specialty  of  sewerage,  Harrison  P. 
Eddy,  Esq.,  C.  E.,  writes  as  follows: 

1.  A  fundamental  economic  consideration  in  the  design  and   con- 
struction of  sewerage  works  is  the  provision  which  shall  be  made  for  the 
future.  The  decision  must  depend  upon  an  opinion  of  the  rate  of  growth 
and  development  of  the  community.    This  opinion  must  be  based  upon 
a  study  of  the  many  natural  conditions,  and  of  the  history  of  other  cities 
similarly  situated,  and  upon  a  consideration  of  the  changes  likely  to  take 
place,  due  to  the  advancing  age  of  the  whole  country,  or  the  portion  of 
the  country  in  which  the  community  is  situated. 

2.  The  quantity  of  sewage  for  which  provision  should  be  made,  must 
be  based  not  only  upon  present  conditions,  but  upon  a  mature  judgment 
as  to  future  conditions,  as  the  requirements  and  demands  of  the  public 
are  constantly  changing  and  at  present  rapidly  increasing.     Too  great 
an  allowance  for  future  growth  results  in  waste.    Too  small  an  allowance 
will  be  equally  disastrous. 

3.  Too  great  provision  for  the  future  may  be  followed  by  difficulties 
in  operation,  resulting  in  unsatisfactory  conditions  or  excessive  operating 
costs. 

4.  Provision  for  run-off  during  storms  must  be  based  not  alone  upon 
rainfall  and  the  estimate  of  the  corresponding  run-off,  but  also  upon  the 
expenditure  which  the  community  can  afford  to  make  for  the  satisfactory 
removal  of  storm  water.    It  may  well  be  that  some  communities  can  better 
afford  to  be  flooded  occasionally,  and  even  to  pay  damages  from  the  public 
treasury  on  account  of  such  flooding,  than  to  go  to  very  large  expense  in 
order  to  avoid  such  occasional  difficulties. 

5.  In  sewage  treatment,  economic  considerations  should  play  as  im- 
portant a  part  as  in  sewerage  and  drainage;  perhaps  even  a  greater  part. 
Here  it  is  necessary  to  balance  the  advantages  obtained  against  the  cost. 
The  engineer  should  not  be  misled  by  aesthetic  considerations  which  may 
lead  him  to  the  conclusion  that  absolutely  no  sewage  and  no  partially 
treated  sewage  should  be  admitted  to  natural  water  courses.    The  expense 
involved  in  attaining  such  an  end  may  be  entirely  out  of  proportion  to 
the  resulting  advantages. 

6.  It  is  important  to  distinguish  between  conditions  which  are  known 
to  be  detrimental  to  public  health,  and  those  which  are  simply  objection- 
able on  aesthetic  grounds.     A  reasonable  expenditure  for  the  protection 
of  the  public  health  should  always  be  advocated.     Nevertheless,  such 
expenditures  should  be  balanced,   and  the  funds  available  should   be 
expended  upon  those  enterprises  which  will  produce  the  greatest  results. 
For  example,  by  a  complete  treatment  of  the  sewage  of  a  municipality, 
the  possibility  of  contracting  typhoid  by  a  few  bathers,  or  a  few  persons 
enjoying  the  water-way  for  pleasure  purposes — such  as  boating — may  be 
avoided.     A  similar  expenditure  in  contagious-diseases  hospitals,  in  the 
fight  against  tuberculosis,  or  in  a  number  of  other  ways,  may  result  in  a 
saving  of  many  times  the  amount  of  sickness  and  death  which  might  be 


*Data  furnished  by  Messrs.  Metcalf  and  Eddy,  consulting  engineers,  Boston,  Mass. 

53 


caused  by  allowing  the  untreated  sewage  to  be  discharged  into  the  neigh- 
boring water  course. 

7.  It  is  important  to  preserve  our  natural  resources.    Every  stream 
or  body  of  water  has  an  economic  value  to  the  community.    If  sewage  is 
allowed  to  be  discharged  into  such  waters,  in  amounts  which  shall  deprive 
us  of  their  use,  we  suffer  an  economic  loss.    It  is,  therefore,  important  to 
measure  these  values  and  balance  them  with  the  cost  of  treating  the  sewage 
to  an  extent  necessary  to  maintain  these  natural  resources  in  a  condition 
which  shall  enable  us  to  take  advantage  of  their  values.    In  some  cases, 
it  will  prove  economical  to  abandon  the  natural  resources  to  the  disposal 
of  sewage  and  industrial  wastes.   In  other  cases,  treatment  necessary  to 
preserve  the  waters  in  suitable  condition  for  our  use  and  enjoyment  will 
involve  expense  much  less  than  "the  value  of  the  waters. 

8.  In  industrial  communities  where  liquid  wastes  must  be  disposed  of, 
other  economic  questions  are  introduced,  such  as  the  value  of  the  indus- 
tries to  the  communities  in  question,  and  the  expense  which  may  be  requir- 
ed of  the  industries,  in  the  treatment  of  their  wastes,  without  the  danger 
of  driving  them  out  of  the  community.    As  in  the  case  of  sewage  disposal, 
the  value  of  the  water-ways  to  the  community  must  be  off-set  against  the 
cost  of  the  treatment  of  the  industrial  wastes;  and  coupled  with  this  bal- 
ance must  be  weighed  the  value  of  the  industry  to  the  community. 

WATER  SUPPLY* 
On  this  subject  Alfred  D.  Flinn,  Esq.,  C.  E.,  writes  as  follows: 

Replying  to  your  letter  of  November  8,  I  am  jotting 
down  below  several  more  or  less  random  questions  which 
occur  in  considering  the  economics  of  water  works.  I  have 
been  unable  to  find  time  to  attempt  to  classify  them  or  even 
to  make  the  list  at  all  complete.  They  are  merely  sugges- 
tions which  have  occurred  off-hand,  and  might  be  described 
as  "Some  Examples  of  Problems  Arising  in  Various  Places 
and  under  Various  Circumstances  in  Connection  with  the 
Economics  of  Water  Works  Projects". 

Possible  extension  of  system  with  growth  of  community 
and  provisions  therefor;  relative  cost  of  each. 

Pumping  from  wells  versus  supply  from  stream  or  lake  by 
gravity. 

Pumping  from  a  nearby  source  versus  gravity  supply  from 
a  distant  source. 

Air-lift  versus  centrifugal  well  pumps. 

Reciprocating  pumping  engines  versus  turbine  pumps,  in- 
cluding cost  of  buildings  and  foundations. 

Filtration  of  a  nearby  impure  supply  versus  a  more  distant 
supply  of  water  of  better  natural  quality. 

A  comparatively  lower-cost  supply  of  hard  water  versus  a 
more  expensive  soft  water,  including  expenditure  by  mem- 
bers of  the  community  for  soap,  boiler  compounds,  etc. 


*Data  furnished  by  Alfred  D.  Plinn,  Esq.,  C.  E.,  deputy  chief  engineer  of  the 
Board  of  Water  Supply,  New  York  City. 

54 


Relative  suitability  and  economy  of  cast-iron,  riveted- 
steel,  welded-steel,  and  wooden  pipes,  depending  upon 
sizes,  prices,  feasibility  of  transportation,  life,  cost  of  re- 
pairs, and  local  conditions  of  water,  soil,  climate,  and  elec- 
trolysis. Economic  sizes  of  pipes,  considering  probable  in- 
crease of  consumption. 

For  large  steel  conduits,  jacketing  with  concrete  and 
lining  with  cement  mortar,  thus  greatly  prolonging  life  and 
materially  increasing  the  hydraulic  capacity,  compared  with 
ordinary  coatings  and  the  roughness  due  to  rivet  heads,  laps 
at  joints,  and  tuberculation. 

Should  very  large  steel  pipes  be  shipped  from  the  shop 
completely  formed  and  coated,  or  the  plates  rolled  to  the 
proper  radius  and  nested,  to  be  riveted  together  in  the  field 
and  there  protected  by  concrete  and  mortar  or  coated? 

Should  filters  be  of  the  slow-sand  type  or  the  rapid-sand 
type?  What  rate  of  filtration  should  be  adopted?  If  rapid 
filters,  what  coagulant?  How  large  should  the  individual 
filter  beds  be,  and  how  should  they  be  grouped? 

What  building  materials  should  be  used  for  pumping 
stations,  gate-houses,  and  other  buildings? 

Should  watersheds  be  owned  outright  and  sources  of  pol- 
lution removed,  or  should  inexpensive  patrols  be  maintained 
to  prevent  the  worst  cases,  and  dependence  be  put  upon  the 
purification  of  the  water  by  filters? 

Can  the  watershed  selected  as  the  source  of  supply  be 
best  developed  by  one  very  large  reservoir  or  by  several 
smaller  reservoirs? 

For  aqueducts  or  large  pipes,  would  a  straighter  and 
shorter  line,  with  tunnels  and  deep  cuts,  be  cheaper  than  a 
longer  line  of  relatively  light  cut-and-cover  construction, 
with  few  or  no  tunnels? 

Should|bottomsf andfslopes  of  impounding  reservoirs  be 
stripped  of  vegetation  and  soil  at  considerable  expense,  or 
should  the  money  be  expended  for  aeration  and  filtration? 


55 


CONCLUSION 

The  speaker  recognizes  clearly  the  numerous  faults  and  deficiencies  of 
his  entire  treatment  of  the  subject  of  "Engineering  Economics"  in  this 
series  of  lectures;  but  he  feels  that  he  has  done  his  best,  considering  all 
the  circumstances  and  the  governing  conditions.  His  hope  is  that  this 
effort  will  be  the  means  of  inducing  other  technical  writers  to  elaborate 
upon  the  subject  and  thus  place  at  the  disposal  of  all  students  of  engineer- 
ing and  all  practicing  engineers  a  vast  fund  of  information  upon  the  main 
general  underlying  principle  which  should  nearly  always  govern  in  the 
conception,  designing,  and  construction  of  all  important  engineering 
work— ECONOMICS. 

It  may  be  of  interest  to  state  that  for  the  last  eighteen  months  the 
speaker  has  been  acting  as  Chairman  of  the  Committee  on  "The  Study 
of  Economics  in  Technical  Schools"  in  the  Society  for  the  Promotion  of 
Engineering  Education;  and  that  he  and  his  co-laborers  have  been  study- 
ing the  question  carefully,  to  the  end  that  they  may  be  able,  at  the  next 
annual  meeting  of  the  society,  to  present  a  report  thereon  which  will  be 
of  real  value,  and  which,  it  is  hoped,  will  be  the  means  of  establishing  the 
study  of  economics  in  all  the  first-class  technical  schools  of  this  country 
upon  a  sound,  logical  basis. 

It  is  the  earnest  wish  of  the  speaker  that  the  work  of  that  committee, 
combined  with  the  effect  of  these  three  lectures,  will  result  in  the  publi- 
cation of  an  exhaustive  standard  treatise  on  "The  Economics  of  Engi- 
neering", prepared  by  the  labor  of  a  large  group  of  prominent  American 
engineers,  selected  from  all  lines  of  technical  activity. 


56 


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